1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Peephole optimize the CFG.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "simplifycfg"
15#include "llvm/Transforms/Utils/Local.h"
16#include "llvm/Constants.h"
17#include "llvm/Instructions.h"
18#include "llvm/IntrinsicInst.h"
19#include "llvm/Type.h"
20#include "llvm/DerivedTypes.h"
21#include "llvm/GlobalVariable.h"
22#include "llvm/Support/CFG.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/Support/raw_ostream.h"
25#include "llvm/Analysis/ConstantFolding.h"
26#include "llvm/Transforms/Utils/BasicBlockUtils.h"
27#include "llvm/ADT/DenseMap.h"
28#include "llvm/ADT/SmallVector.h"
29#include "llvm/ADT/SmallPtrSet.h"
30#include "llvm/ADT/Statistic.h"
31#include <algorithm>
32#include <functional>
33#include <set>
34#include <map>
35using namespace llvm;
36
37STATISTIC(NumSpeculations, "Number of speculative executed instructions");
38
39/// SafeToMergeTerminators - Return true if it is safe to merge these two
40/// terminator instructions together.
41///
42static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
43 if (SI1 == SI2) return false; // Can't merge with self!
44
45 // It is not safe to merge these two switch instructions if they have a common
46 // successor, and if that successor has a PHI node, and if *that* PHI node has
47 // conflicting incoming values from the two switch blocks.
48 BasicBlock *SI1BB = SI1->getParent();
49 BasicBlock *SI2BB = SI2->getParent();
50 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
51
52 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
53 if (SI1Succs.count(*I))
54 for (BasicBlock::iterator BBI = (*I)->begin();
55 isa<PHINode>(BBI); ++BBI) {
56 PHINode *PN = cast<PHINode>(BBI);
57 if (PN->getIncomingValueForBlock(SI1BB) !=
58 PN->getIncomingValueForBlock(SI2BB))
59 return false;
60 }
61
62 return true;
63}
64
65/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
66/// now be entries in it from the 'NewPred' block. The values that will be
67/// flowing into the PHI nodes will be the same as those coming in from
68/// ExistPred, an existing predecessor of Succ.
69static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
70 BasicBlock *ExistPred) {
71 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
72 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
73 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
74
75 PHINode *PN;
76 for (BasicBlock::iterator I = Succ->begin();
77 (PN = dyn_cast<PHINode>(I)); ++I)
78 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
79}
80
81
82/// GetIfCondition - Given a basic block (BB) with two predecessors (and
83/// presumably PHI nodes in it), check to see if the merge at this block is due
84/// to an "if condition". If so, return the boolean condition that determines
85/// which entry into BB will be taken. Also, return by references the block
86/// that will be entered from if the condition is true, and the block that will
87/// be entered if the condition is false.
88///
89///
90static Value *GetIfCondition(BasicBlock *BB,
91 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
92 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
93 "Function can only handle blocks with 2 predecessors!");
94 BasicBlock *Pred1 = *pred_begin(BB);
95 BasicBlock *Pred2 = *++pred_begin(BB);
96
97 // We can only handle branches. Other control flow will be lowered to
98 // branches if possible anyway.
99 if (!isa<BranchInst>(Pred1->getTerminator()) ||
100 !isa<BranchInst>(Pred2->getTerminator()))
101 return 0;
102 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
103 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
104
105 // Eliminate code duplication by ensuring that Pred1Br is conditional if
106 // either are.
107 if (Pred2Br->isConditional()) {
108 // If both branches are conditional, we don't have an "if statement". In
109 // reality, we could transform this case, but since the condition will be
110 // required anyway, we stand no chance of eliminating it, so the xform is
111 // probably not profitable.
112 if (Pred1Br->isConditional())
113 return 0;
114
115 std::swap(Pred1, Pred2);
116 std::swap(Pred1Br, Pred2Br);
117 }
118
119 if (Pred1Br->isConditional()) {
120 // If we found a conditional branch predecessor, make sure that it branches
121 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
122 if (Pred1Br->getSuccessor(0) == BB &&
123 Pred1Br->getSuccessor(1) == Pred2) {
124 IfTrue = Pred1;
125 IfFalse = Pred2;
126 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
127 Pred1Br->getSuccessor(1) == BB) {
128 IfTrue = Pred2;
129 IfFalse = Pred1;
130 } else {
131 // We know that one arm of the conditional goes to BB, so the other must
132 // go somewhere unrelated, and this must not be an "if statement".
133 return 0;
134 }
135
136 // The only thing we have to watch out for here is to make sure that Pred2
137 // doesn't have incoming edges from other blocks. If it does, the condition
138 // doesn't dominate BB.
139 if (++pred_begin(Pred2) != pred_end(Pred2))
140 return 0;
141
142 return Pred1Br->getCondition();
143 }
144
145 // Ok, if we got here, both predecessors end with an unconditional branch to
146 // BB. Don't panic! If both blocks only have a single (identical)
147 // predecessor, and THAT is a conditional branch, then we're all ok!
148 if (pred_begin(Pred1) == pred_end(Pred1) ||
149 ++pred_begin(Pred1) != pred_end(Pred1) ||
150 pred_begin(Pred2) == pred_end(Pred2) ||
151 ++pred_begin(Pred2) != pred_end(Pred2) ||
152 *pred_begin(Pred1) != *pred_begin(Pred2))
153 return 0;
154
155 // Otherwise, if this is a conditional branch, then we can use it!
156 BasicBlock *CommonPred = *pred_begin(Pred1);
157 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
158 assert(BI->isConditional() && "Two successors but not conditional?");
159 if (BI->getSuccessor(0) == Pred1) {
160 IfTrue = Pred1;
161 IfFalse = Pred2;
162 } else {
163 IfTrue = Pred2;
164 IfFalse = Pred1;
165 }
166 return BI->getCondition();
167 }
168 return 0;
169}
170
171/// DominatesMergePoint - If we have a merge point of an "if condition" as
172/// accepted above, return true if the specified value dominates the block. We
173/// don't handle the true generality of domination here, just a special case
174/// which works well enough for us.
175///
176/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
177/// see if V (which must be an instruction) is cheap to compute and is
178/// non-trapping. If both are true, the instruction is inserted into the set
179/// and true is returned.
180static bool DominatesMergePoint(Value *V, BasicBlock *BB,
181 std::set<Instruction*> *AggressiveInsts) {
182 Instruction *I = dyn_cast<Instruction>(V);
183 if (!I) {
184 // Non-instructions all dominate instructions, but not all constantexprs
185 // can be executed unconditionally.
186 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
187 if (C->canTrap())
188 return false;
189 return true;
190 }
191 BasicBlock *PBB = I->getParent();
192
193 // We don't want to allow weird loops that might have the "if condition" in
194 // the bottom of this block.
195 if (PBB == BB) return false;
196
197 // If this instruction is defined in a block that contains an unconditional
198 // branch to BB, then it must be in the 'conditional' part of the "if
199 // statement".
200 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
201 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
202 if (!AggressiveInsts) return false;
203 // Okay, it looks like the instruction IS in the "condition". Check to
204 // see if its a cheap instruction to unconditionally compute, and if it
205 // only uses stuff defined outside of the condition. If so, hoist it out.
206 if (!I->isSafeToSpeculativelyExecute())
207 return false;
208
209 switch (I->getOpcode()) {
210 default: return false; // Cannot hoist this out safely.
211 case Instruction::Load: {
212 // We have to check to make sure there are no instructions before the
213 // load in its basic block, as we are going to hoist the loop out to
214 // its predecessor.
215 BasicBlock::iterator IP = PBB->begin();
216 while (isa<DbgInfoIntrinsic>(IP))
217 IP++;
218 if (IP != BasicBlock::iterator(I))
219 return false;
220 break;
221 }
222 case Instruction::Add:
223 case Instruction::Sub:
224 case Instruction::And:
225 case Instruction::Or:
226 case Instruction::Xor:
227 case Instruction::Shl:
228 case Instruction::LShr:
229 case Instruction::AShr:
230 case Instruction::ICmp:
231 break; // These are all cheap and non-trapping instructions.
232 }
233
234 // Okay, we can only really hoist these out if their operands are not
235 // defined in the conditional region.
236 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
237 if (!DominatesMergePoint(*i, BB, 0))
238 return false;
239 // Okay, it's safe to do this! Remember this instruction.
240 AggressiveInsts->insert(I);
241 }
242
243 return true;
244}
245
246/// GatherConstantSetEQs - Given a potentially 'or'd together collection of
247/// icmp_eq instructions that compare a value against a constant, return the
248/// value being compared, and stick the constant into the Values vector.
249static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
250 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
251 if (Inst->getOpcode() == Instruction::ICmp &&
252 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
253 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
254 Values.push_back(C);
255 return Inst->getOperand(0);
256 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
257 Values.push_back(C);
258 return Inst->getOperand(1);
259 }
260 } else if (Inst->getOpcode() == Instruction::Or) {
261 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
262 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
263 if (LHS == RHS)
264 return LHS;
265 }
266 }
267 return 0;
268}
269
270/// GatherConstantSetNEs - Given a potentially 'and'd together collection of
271/// setne instructions that compare a value against a constant, return the value
272/// being compared, and stick the constant into the Values vector.
273static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
274 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
275 if (Inst->getOpcode() == Instruction::ICmp &&
276 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
277 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
278 Values.push_back(C);
279 return Inst->getOperand(0);
280 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
281 Values.push_back(C);
282 return Inst->getOperand(1);
283 }
284 } else if (Inst->getOpcode() == Instruction::And) {
285 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
286 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
287 if (LHS == RHS)
288 return LHS;
289 }
290 }
291 return 0;
292}
293
294/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
295/// bunch of comparisons of one value against constants, return the value and
296/// the constants being compared.
297static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
298 std::vector<ConstantInt*> &Values) {
299 if (Cond->getOpcode() == Instruction::Or) {
300 CompVal = GatherConstantSetEQs(Cond, Values);
301
302 // Return true to indicate that the condition is true if the CompVal is
303 // equal to one of the constants.
304 return true;
305 } else if (Cond->getOpcode() == Instruction::And) {
306 CompVal = GatherConstantSetNEs(Cond, Values);
307
308 // Return false to indicate that the condition is false if the CompVal is
309 // equal to one of the constants.
310 return false;
311 }
312 return false;
313}
314
315static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
316 Instruction* Cond = 0;
317 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
318 Cond = dyn_cast<Instruction>(SI->getCondition());
319 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
320 if (BI->isConditional())
321 Cond = dyn_cast<Instruction>(BI->getCondition());
322 }
323
324 TI->eraseFromParent();
325 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
326}
327
328/// isValueEqualityComparison - Return true if the specified terminator checks
329/// to see if a value is equal to constant integer value.
330static Value *isValueEqualityComparison(TerminatorInst *TI) {
331 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
332 // Do not permit merging of large switch instructions into their
333 // predecessors unless there is only one predecessor.
334 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
335 pred_end(SI->getParent())) > 128)
336 return 0;
337
338 return SI->getCondition();
339 }
340 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
341 if (BI->isConditional() && BI->getCondition()->hasOneUse())
342 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
343 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
344 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
345 isa<ConstantInt>(ICI->getOperand(1)))
346 return ICI->getOperand(0);
347 return 0;
348}
349
350/// GetValueEqualityComparisonCases - Given a value comparison instruction,
351/// decode all of the 'cases' that it represents and return the 'default' block.
352static BasicBlock *
353GetValueEqualityComparisonCases(TerminatorInst *TI,
354 std::vector<std::pair<ConstantInt*,
355 BasicBlock*> > &Cases) {
356 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
357 Cases.reserve(SI->getNumCases());
358 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
359 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
360 return SI->getDefaultDest();
361 }
362
363 BranchInst *BI = cast<BranchInst>(TI);
364 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
365 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
366 BI->getSuccessor(ICI->getPredicate() ==
367 ICmpInst::ICMP_NE)));
368 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
369}
370
371
372/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
373/// in the list that match the specified block.
374static void EliminateBlockCases(BasicBlock *BB,
375 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
376 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
377 if (Cases[i].second == BB) {
378 Cases.erase(Cases.begin()+i);
379 --i; --e;
380 }
381}
382
383/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
384/// well.
385static bool
386ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
387 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
388 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
389
390 // Make V1 be smaller than V2.
391 if (V1->size() > V2->size())
392 std::swap(V1, V2);
393
394 if (V1->size() == 0) return false;
395 if (V1->size() == 1) {
396 // Just scan V2.
397 ConstantInt *TheVal = (*V1)[0].first;
398 for (unsigned i = 0, e = V2->size(); i != e; ++i)
399 if (TheVal == (*V2)[i].first)
400 return true;
401 }
402
403 // Otherwise, just sort both lists and compare element by element.
404 std::sort(V1->begin(), V1->end());
405 std::sort(V2->begin(), V2->end());
406 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
407 while (i1 != e1 && i2 != e2) {
408 if ((*V1)[i1].first == (*V2)[i2].first)
409 return true;
410 if ((*V1)[i1].first < (*V2)[i2].first)
411 ++i1;
412 else
413 ++i2;
414 }
415 return false;
416}
417
418/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
419/// terminator instruction and its block is known to only have a single
420/// predecessor block, check to see if that predecessor is also a value
421/// comparison with the same value, and if that comparison determines the
422/// outcome of this comparison. If so, simplify TI. This does a very limited
423/// form of jump threading.
424static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
425 BasicBlock *Pred) {
426 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
427 if (!PredVal) return false; // Not a value comparison in predecessor.
428
429 Value *ThisVal = isValueEqualityComparison(TI);
430 assert(ThisVal && "This isn't a value comparison!!");
431 if (ThisVal != PredVal) return false; // Different predicates.
432
433 // Find out information about when control will move from Pred to TI's block.
434 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
435 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
436 PredCases);
437 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
438
439 // Find information about how control leaves this block.
440 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
441 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
442 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
443
444 // If TI's block is the default block from Pred's comparison, potentially
445 // simplify TI based on this knowledge.
446 if (PredDef == TI->getParent()) {
447 // If we are here, we know that the value is none of those cases listed in
448 // PredCases. If there are any cases in ThisCases that are in PredCases, we
449 // can simplify TI.
450 if (ValuesOverlap(PredCases, ThisCases)) {
451 if (isa<BranchInst>(TI)) {
452 // Okay, one of the successors of this condbr is dead. Convert it to a
453 // uncond br.
454 assert(ThisCases.size() == 1 && "Branch can only have one case!");
455 // Insert the new branch.
456 Instruction *NI = BranchInst::Create(ThisDef, TI);
457 (void) NI;
458
459 // Remove PHI node entries for the dead edge.
460 ThisCases[0].second->removePredecessor(TI->getParent());
461
462 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
463 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
464
465 EraseTerminatorInstAndDCECond(TI);
466 return true;
467
468 } else {
469 SwitchInst *SI = cast<SwitchInst>(TI);
470 // Okay, TI has cases that are statically dead, prune them away.
471 SmallPtrSet<Constant*, 16> DeadCases;
472 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
473 DeadCases.insert(PredCases[i].first);
474
475 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
476 << "Through successor TI: " << *TI);
477
478 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
479 if (DeadCases.count(SI->getCaseValue(i))) {
480 SI->getSuccessor(i)->removePredecessor(TI->getParent());
481 SI->removeCase(i);
482 }
483
484 DEBUG(errs() << "Leaving: " << *TI << "\n");
485 return true;
486 }
487 }
488
489 } else {
490 // Otherwise, TI's block must correspond to some matched value. Find out
491 // which value (or set of values) this is.
492 ConstantInt *TIV = 0;
493 BasicBlock *TIBB = TI->getParent();
494 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
495 if (PredCases[i].second == TIBB) {
496 if (TIV == 0)
497 TIV = PredCases[i].first;
498 else
499 return false; // Cannot handle multiple values coming to this block.
500 }
501 assert(TIV && "No edge from pred to succ?");
502
503 // Okay, we found the one constant that our value can be if we get into TI's
504 // BB. Find out which successor will unconditionally be branched to.
505 BasicBlock *TheRealDest = 0;
506 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
507 if (ThisCases[i].first == TIV) {
508 TheRealDest = ThisCases[i].second;
509 break;
510 }
511
512 // If not handled by any explicit cases, it is handled by the default case.
513 if (TheRealDest == 0) TheRealDest = ThisDef;
514
515 // Remove PHI node entries for dead edges.
516 BasicBlock *CheckEdge = TheRealDest;
517 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
518 if (*SI != CheckEdge)
519 (*SI)->removePredecessor(TIBB);
520 else
521 CheckEdge = 0;
522
523 // Insert the new branch.
524 Instruction *NI = BranchInst::Create(TheRealDest, TI);
525 (void) NI;
526
527 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
528 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
529
530 EraseTerminatorInstAndDCECond(TI);
531 return true;
532 }
533 return false;
534}
535
536namespace {
537 /// ConstantIntOrdering - This class implements a stable ordering of constant
538 /// integers that does not depend on their address. This is important for
539 /// applications that sort ConstantInt's to ensure uniqueness.
540 struct ConstantIntOrdering {
541 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
542 return LHS->getValue().ult(RHS->getValue());
543 }
544 };
545}
546
547/// FoldValueComparisonIntoPredecessors - The specified terminator is a value
548/// equality comparison instruction (either a switch or a branch on "X == c").
549/// See if any of the predecessors of the terminator block are value comparisons
550/// on the same value. If so, and if safe to do so, fold them together.
551static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
552 BasicBlock *BB = TI->getParent();
553 Value *CV = isValueEqualityComparison(TI); // CondVal
554 assert(CV && "Not a comparison?");
555 bool Changed = false;
556
557 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
558 while (!Preds.empty()) {
559 BasicBlock *Pred = Preds.pop_back_val();
560
561 // See if the predecessor is a comparison with the same value.
562 TerminatorInst *PTI = Pred->getTerminator();
563 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
564
565 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
566 // Figure out which 'cases' to copy from SI to PSI.
567 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
568 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
569
570 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
571 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
572
573 // Based on whether the default edge from PTI goes to BB or not, fill in
574 // PredCases and PredDefault with the new switch cases we would like to
575 // build.
576 SmallVector<BasicBlock*, 8> NewSuccessors;
577
578 if (PredDefault == BB) {
579 // If this is the default destination from PTI, only the edges in TI
580 // that don't occur in PTI, or that branch to BB will be activated.
581 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
582 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
583 if (PredCases[i].second != BB)
584 PTIHandled.insert(PredCases[i].first);
585 else {
586 // The default destination is BB, we don't need explicit targets.
587 std::swap(PredCases[i], PredCases.back());
588 PredCases.pop_back();
589 --i; --e;
590 }
591
592 // Reconstruct the new switch statement we will be building.
593 if (PredDefault != BBDefault) {
594 PredDefault->removePredecessor(Pred);
595 PredDefault = BBDefault;
596 NewSuccessors.push_back(BBDefault);
597 }
598 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
599 if (!PTIHandled.count(BBCases[i].first) &&
600 BBCases[i].second != BBDefault) {
601 PredCases.push_back(BBCases[i]);
602 NewSuccessors.push_back(BBCases[i].second);
603 }
604
605 } else {
606 // If this is not the default destination from PSI, only the edges
607 // in SI that occur in PSI with a destination of BB will be
608 // activated.
609 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
610 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
611 if (PredCases[i].second == BB) {
612 PTIHandled.insert(PredCases[i].first);
613 std::swap(PredCases[i], PredCases.back());
614 PredCases.pop_back();
615 --i; --e;
616 }
617
618 // Okay, now we know which constants were sent to BB from the
619 // predecessor. Figure out where they will all go now.
620 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
621 if (PTIHandled.count(BBCases[i].first)) {
622 // If this is one we are capable of getting...
623 PredCases.push_back(BBCases[i]);
624 NewSuccessors.push_back(BBCases[i].second);
625 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
626 }
627
628 // If there are any constants vectored to BB that TI doesn't handle,
629 // they must go to the default destination of TI.
630 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
631 PTIHandled.begin(),
632 E = PTIHandled.end(); I != E; ++I) {
633 PredCases.push_back(std::make_pair(*I, BBDefault));
634 NewSuccessors.push_back(BBDefault);
635 }
636 }
637
638 // Okay, at this point, we know which new successor Pred will get. Make
639 // sure we update the number of entries in the PHI nodes for these
640 // successors.
641 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
642 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
643
644 // Now that the successors are updated, create the new Switch instruction.
645 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
646 PredCases.size(), PTI);
647 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
648 NewSI->addCase(PredCases[i].first, PredCases[i].second);
649
650 EraseTerminatorInstAndDCECond(PTI);
651
652 // Okay, last check. If BB is still a successor of PSI, then we must
653 // have an infinite loop case. If so, add an infinitely looping block
654 // to handle the case to preserve the behavior of the code.
655 BasicBlock *InfLoopBlock = 0;
656 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
657 if (NewSI->getSuccessor(i) == BB) {
658 if (InfLoopBlock == 0) {
659 // Insert it at the end of the function, because it's either code,
660 // or it won't matter if it's hot. :)
661 InfLoopBlock = BasicBlock::Create(BB->getContext(),
662 "infloop", BB->getParent());
663 BranchInst::Create(InfLoopBlock, InfLoopBlock);
664 }
665 NewSI->setSuccessor(i, InfLoopBlock);
666 }
667
668 Changed = true;
669 }
670 }
671 return Changed;
672}
673
674// isSafeToHoistInvoke - If we would need to insert a select that uses the
675// value of this invoke (comments in HoistThenElseCodeToIf explain why we
676// would need to do this), we can't hoist the invoke, as there is nowhere
677// to put the select in this case.
678static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
679 Instruction *I1, Instruction *I2) {
680 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
681 PHINode *PN;
682 for (BasicBlock::iterator BBI = SI->begin();
683 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
684 Value *BB1V = PN->getIncomingValueForBlock(BB1);
685 Value *BB2V = PN->getIncomingValueForBlock(BB2);
686 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
687 return false;
688 }
689 }
690 }
691 return true;
692}
693
694/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
695/// BB2, hoist any common code in the two blocks up into the branch block. The
696/// caller of this function guarantees that BI's block dominates BB1 and BB2.
697static bool HoistThenElseCodeToIf(BranchInst *BI) {
698 // This does very trivial matching, with limited scanning, to find identical
699 // instructions in the two blocks. In particular, we don't want to get into
700 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
701 // such, we currently just scan for obviously identical instructions in an
702 // identical order.
703 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
704 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
705
706 BasicBlock::iterator BB1_Itr = BB1->begin();
707 BasicBlock::iterator BB2_Itr = BB2->begin();
708
709 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
710 while (isa<DbgInfoIntrinsic>(I1))
711 I1 = BB1_Itr++;
712 while (isa<DbgInfoIntrinsic>(I2))
713 I2 = BB2_Itr++;
714 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
715 !I1->isIdenticalToWhenDefined(I2) ||
716 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
717 return false;
718
719 // If we get here, we can hoist at least one instruction.
720 BasicBlock *BIParent = BI->getParent();
721
722 do {
723 // If we are hoisting the terminator instruction, don't move one (making a
724 // broken BB), instead clone it, and remove BI.
725 if (isa<TerminatorInst>(I1))
726 goto HoistTerminator;
727
728 // For a normal instruction, we just move one to right before the branch,
729 // then replace all uses of the other with the first. Finally, we remove
730 // the now redundant second instruction.
731 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
732 if (!I2->use_empty())
733 I2->replaceAllUsesWith(I1);
734 I1->intersectOptionalDataWith(I2);
735 BB2->getInstList().erase(I2);
736
737 I1 = BB1_Itr++;
738 while (isa<DbgInfoIntrinsic>(I1))
739 I1 = BB1_Itr++;
740 I2 = BB2_Itr++;
741 while (isa<DbgInfoIntrinsic>(I2))
742 I2 = BB2_Itr++;
743 } while (I1->getOpcode() == I2->getOpcode() &&
744 I1->isIdenticalToWhenDefined(I2));
745
746 return true;
747
748HoistTerminator:
749 // It may not be possible to hoist an invoke.
750 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
751 return true;
752
753 // Okay, it is safe to hoist the terminator.
754 Instruction *NT = I1->clone();
755 BIParent->getInstList().insert(BI, NT);
756 if (NT->getType() != Type::getVoidTy(BB1->getContext())) {
757 I1->replaceAllUsesWith(NT);
758 I2->replaceAllUsesWith(NT);
759 NT->takeName(I1);
760 }
761
762 // Hoisting one of the terminators from our successor is a great thing.
763 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
764 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
765 // nodes, so we insert select instruction to compute the final result.
766 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
767 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
768 PHINode *PN;
769 for (BasicBlock::iterator BBI = SI->begin();
770 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
771 Value *BB1V = PN->getIncomingValueForBlock(BB1);
772 Value *BB2V = PN->getIncomingValueForBlock(BB2);
773 if (BB1V != BB2V) {
774 // These values do not agree. Insert a select instruction before NT
775 // that determines the right value.
776 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
777 if (SI == 0)
778 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
779 BB1V->getName()+"."+BB2V->getName(), NT);
780 // Make the PHI node use the select for all incoming values for BB1/BB2
781 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
782 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
783 PN->setIncomingValue(i, SI);
784 }
785 }
786 }
787
788 // Update any PHI nodes in our new successors.
789 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
790 AddPredecessorToBlock(*SI, BIParent, BB1);
791
792 EraseTerminatorInstAndDCECond(BI);
793 return true;
794}
795
796/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
797/// and an BB2 and the only successor of BB1 is BB2, hoist simple code
798/// (for now, restricted to a single instruction that's side effect free) from
799/// the BB1 into the branch block to speculatively execute it.
800static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
801 // Only speculatively execution a single instruction (not counting the
802 // terminator) for now.
803 Instruction *HInst = NULL;
804 Instruction *Term = BB1->getTerminator();
805 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
806 BBI != BBE; ++BBI) {
807 Instruction *I = BBI;
808 // Skip debug info.
809 if (isa<DbgInfoIntrinsic>(I)) continue;
810 if (I == Term) break;
811
812 if (!HInst)
813 HInst = I;
814 else
815 return false;
816 }
817 if (!HInst)
818 return false;
819
820 // Be conservative for now. FP select instruction can often be expensive.
821 Value *BrCond = BI->getCondition();
822 if (isa<Instruction>(BrCond) &&
823 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
824 return false;
825
826 // If BB1 is actually on the false edge of the conditional branch, remember
827 // to swap the select operands later.
828 bool Invert = false;
829 if (BB1 != BI->getSuccessor(0)) {
830 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
831 Invert = true;
832 }
833
834 // Turn
835 // BB:
836 // %t1 = icmp
837 // br i1 %t1, label %BB1, label %BB2
838 // BB1:
839 // %t3 = add %t2, c
840 // br label BB2
841 // BB2:
842 // =>
843 // BB:
844 // %t1 = icmp
845 // %t4 = add %t2, c
846 // %t3 = select i1 %t1, %t2, %t3
847 switch (HInst->getOpcode()) {
848 default: return false; // Not safe / profitable to hoist.
849 case Instruction::Add:
850 case Instruction::Sub:
851 // Not worth doing for vector ops.
852 if (isa<VectorType>(HInst->getType()))
853 return false;
854 break;
855 case Instruction::And:
856 case Instruction::Or:
857 case Instruction::Xor:
858 case Instruction::Shl:
859 case Instruction::LShr:
860 case Instruction::AShr:
861 // Don't mess with vector operations.
862 if (isa<VectorType>(HInst->getType()))
863 return false;
864 break; // These are all cheap and non-trapping instructions.
865 }
866
867 // If the instruction is obviously dead, don't try to predicate it.
868 if (HInst->use_empty()) {
869 HInst->eraseFromParent();
870 return true;
871 }
872
873 // Can we speculatively execute the instruction? And what is the value
874 // if the condition is false? Consider the phi uses, if the incoming value
875 // from the "if" block are all the same V, then V is the value of the
876 // select if the condition is false.
877 BasicBlock *BIParent = BI->getParent();
878 SmallVector<PHINode*, 4> PHIUses;
879 Value *FalseV = NULL;
880
881 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
882 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
883 UI != E; ++UI) {
884 // Ignore any user that is not a PHI node in BB2. These can only occur in
885 // unreachable blocks, because they would not be dominated by the instr.
886 PHINode *PN = dyn_cast<PHINode>(UI);
887 if (!PN || PN->getParent() != BB2)
888 return false;
889 PHIUses.push_back(PN);
890
891 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
892 if (!FalseV)
893 FalseV = PHIV;
894 else if (FalseV != PHIV)
895 return false; // Inconsistent value when condition is false.
896 }
897
898 assert(FalseV && "Must have at least one user, and it must be a PHI");
899
900 // Do not hoist the instruction if any of its operands are defined but not
901 // used in this BB. The transformation will prevent the operand from
902 // being sunk into the use block.
903 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
904 i != e; ++i) {
905 Instruction *OpI = dyn_cast<Instruction>(*i);
906 if (OpI && OpI->getParent() == BIParent &&
907 !OpI->isUsedInBasicBlock(BIParent))
908 return false;
909 }
910
911 // If we get here, we can hoist the instruction. Try to place it
912 // before the icmp instruction preceding the conditional branch.
913 BasicBlock::iterator InsertPos = BI;
914 if (InsertPos != BIParent->begin())
915 --InsertPos;
916 // Skip debug info between condition and branch.
917 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
918 --InsertPos;
919 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
920 SmallPtrSet<Instruction *, 4> BB1Insns;
921 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
922 BB1I != BB1E; ++BB1I)
923 BB1Insns.insert(BB1I);
924 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
925 UI != UE; ++UI) {
926 Instruction *Use = cast<Instruction>(*UI);
927 if (BB1Insns.count(Use)) {
928 // If BrCond uses the instruction that place it just before
929 // branch instruction.
930 InsertPos = BI;
931 break;
932 }
933 }
934 } else
935 InsertPos = BI;
936 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
937
938 // Create a select whose true value is the speculatively executed value and
939 // false value is the previously determined FalseV.
940 SelectInst *SI;
941 if (Invert)
942 SI = SelectInst::Create(BrCond, FalseV, HInst,
943 FalseV->getName() + "." + HInst->getName(), BI);
944 else
945 SI = SelectInst::Create(BrCond, HInst, FalseV,
946 HInst->getName() + "." + FalseV->getName(), BI);
947
948 // Make the PHI node use the select for all incoming values for "then" and
949 // "if" blocks.
950 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
951 PHINode *PN = PHIUses[i];
952 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
953 if (PN->getIncomingBlock(j) == BB1 ||
954 PN->getIncomingBlock(j) == BIParent)
955 PN->setIncomingValue(j, SI);
956 }
957
958 ++NumSpeculations;
959 return true;
960}
961
962/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
963/// across this block.
964static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
965 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
966 unsigned Size = 0;
967
968 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
969 if (isa<DbgInfoIntrinsic>(BBI))
970 continue;
971 if (Size > 10) return false; // Don't clone large BB's.
972 ++Size;
973
974 // We can only support instructions that do not define values that are
975 // live outside of the current basic block.
976 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
977 UI != E; ++UI) {
978 Instruction *U = cast<Instruction>(*UI);
979 if (U->getParent() != BB || isa<PHINode>(U)) return false;
980 }
981
982 // Looks ok, continue checking.
983 }
984
985 return true;
986}
987
988/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
989/// that is defined in the same block as the branch and if any PHI entries are
990/// constants, thread edges corresponding to that entry to be branches to their
991/// ultimate destination.
992static bool FoldCondBranchOnPHI(BranchInst *BI) {
993 BasicBlock *BB = BI->getParent();
994 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
995 // NOTE: we currently cannot transform this case if the PHI node is used
996 // outside of the block.
997 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
998 return false;
999
1000 // Degenerate case of a single entry PHI.
1001 if (PN->getNumIncomingValues() == 1) {
1002 FoldSingleEntryPHINodes(PN->getParent());
1003 return true;
1004 }
1005
1006 // Now we know that this block has multiple preds and two succs.
1007 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1008
1009 // Okay, this is a simple enough basic block. See if any phi values are
1010 // constants.
1011 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1012 ConstantInt *CB;
1013 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1014 CB->getType() == Type::getInt1Ty(BB->getContext())) {
1015 // Okay, we now know that all edges from PredBB should be revectored to
1016 // branch to RealDest.
1017 BasicBlock *PredBB = PN->getIncomingBlock(i);
1018 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1019
1020 if (RealDest == BB) continue; // Skip self loops.
1021
1022 // The dest block might have PHI nodes, other predecessors and other
1023 // difficult cases. Instead of being smart about this, just insert a new
1024 // block that jumps to the destination block, effectively splitting
1025 // the edge we are about to create.
1026 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1027 RealDest->getName()+".critedge",
1028 RealDest->getParent(), RealDest);
1029 BranchInst::Create(RealDest, EdgeBB);
1030 PHINode *PN;
1031 for (BasicBlock::iterator BBI = RealDest->begin();
1032 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1033 Value *V = PN->getIncomingValueForBlock(BB);
1034 PN->addIncoming(V, EdgeBB);
1035 }
1036
1037 // BB may have instructions that are being threaded over. Clone these
1038 // instructions into EdgeBB. We know that there will be no uses of the
1039 // cloned instructions outside of EdgeBB.
1040 BasicBlock::iterator InsertPt = EdgeBB->begin();
1041 std::map<Value*, Value*> TranslateMap; // Track translated values.
1042 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1043 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1044 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1045 } else {
1046 // Clone the instruction.
1047 Instruction *N = BBI->clone();
1048 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1049
1050 // Update operands due to translation.
1051 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1052 i != e; ++i) {
1053 std::map<Value*, Value*>::iterator PI =
1054 TranslateMap.find(*i);
1055 if (PI != TranslateMap.end())
1056 *i = PI->second;
1057 }
1058
1059 // Check for trivial simplification.
1060 if (Constant *C = ConstantFoldInstruction(N)) {
1061 TranslateMap[BBI] = C;
1062 delete N; // Constant folded away, don't need actual inst
1063 } else {
1064 // Insert the new instruction into its new home.
1065 EdgeBB->getInstList().insert(InsertPt, N);
1066 if (!BBI->use_empty())
1067 TranslateMap[BBI] = N;
1068 }
1069 }
1070 }
1071
1072 // Loop over all of the edges from PredBB to BB, changing them to branch
1073 // to EdgeBB instead.
1074 TerminatorInst *PredBBTI = PredBB->getTerminator();
1075 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1076 if (PredBBTI->getSuccessor(i) == BB) {
1077 BB->removePredecessor(PredBB);
1078 PredBBTI->setSuccessor(i, EdgeBB);
1079 }
1080
1081 // Recurse, simplifying any other constants.
1082 return FoldCondBranchOnPHI(BI) | true;
1083 }
1084 }
1085
1086 return false;
1087}
1088
1089/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1090/// PHI node, see if we can eliminate it.
1091static bool FoldTwoEntryPHINode(PHINode *PN) {
1092 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1093 // statement", which has a very simple dominance structure. Basically, we
1094 // are trying to find the condition that is being branched on, which
1095 // subsequently causes this merge to happen. We really want control
1096 // dependence information for this check, but simplifycfg can't keep it up
1097 // to date, and this catches most of the cases we care about anyway.
1098 //
1099 BasicBlock *BB = PN->getParent();
1100 BasicBlock *IfTrue, *IfFalse;
1101 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1102 if (!IfCond) return false;
1103
1104 // Okay, we found that we can merge this two-entry phi node into a select.
1105 // Doing so would require us to fold *all* two entry phi nodes in this block.
1106 // At some point this becomes non-profitable (particularly if the target
1107 // doesn't support cmov's). Only do this transformation if there are two or
1108 // fewer PHI nodes in this block.
1109 unsigned NumPhis = 0;
1110 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1111 if (NumPhis > 2)
1112 return false;
1113
1114 DEBUG(errs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1115 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1116
1117 // Loop over the PHI's seeing if we can promote them all to select
1118 // instructions. While we are at it, keep track of the instructions
1119 // that need to be moved to the dominating block.
1120 std::set<Instruction*> AggressiveInsts;
1121
1122 BasicBlock::iterator AfterPHIIt = BB->begin();
1123 while (isa<PHINode>(AfterPHIIt)) {
1124 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1125 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1126 if (PN->getIncomingValue(0) != PN)
1127 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1128 else
1129 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1130 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1131 &AggressiveInsts) ||
1132 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1133 &AggressiveInsts)) {
1134 return false;
1135 }
1136 }
1137
1138 // If we all PHI nodes are promotable, check to make sure that all
1139 // instructions in the predecessor blocks can be promoted as well. If
1140 // not, we won't be able to get rid of the control flow, so it's not
1141 // worth promoting to select instructions.
1142 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1143 PN = cast<PHINode>(BB->begin());
1144 BasicBlock *Pred = PN->getIncomingBlock(0);
1145 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1146 IfBlock1 = Pred;
1147 DomBlock = *pred_begin(Pred);
1148 for (BasicBlock::iterator I = Pred->begin();
1149 !isa<TerminatorInst>(I); ++I)
1150 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1151 // This is not an aggressive instruction that we can promote.
1152 // Because of this, we won't be able to get rid of the control
1153 // flow, so the xform is not worth it.
1154 return false;
1155 }
1156 }
1157
1158 Pred = PN->getIncomingBlock(1);
1159 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1160 IfBlock2 = Pred;
1161 DomBlock = *pred_begin(Pred);
1162 for (BasicBlock::iterator I = Pred->begin();
1163 !isa<TerminatorInst>(I); ++I)
1164 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1165 // This is not an aggressive instruction that we can promote.
1166 // Because of this, we won't be able to get rid of the control
1167 // flow, so the xform is not worth it.
1168 return false;
1169 }
1170 }
1171
1172 // If we can still promote the PHI nodes after this gauntlet of tests,
1173 // do all of the PHI's now.
1174
1175 // Move all 'aggressive' instructions, which are defined in the
1176 // conditional parts of the if's up to the dominating block.
1177 if (IfBlock1) {
1178 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1179 IfBlock1->getInstList(),
1180 IfBlock1->begin(),
1181 IfBlock1->getTerminator());
1182 }
1183 if (IfBlock2) {
1184 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1185 IfBlock2->getInstList(),
1186 IfBlock2->begin(),
1187 IfBlock2->getTerminator());
1188 }
1189
1190 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1191 // Change the PHI node into a select instruction.
1192 Value *TrueVal =
1193 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1194 Value *FalseVal =
1195 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1196
1197 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1198 PN->replaceAllUsesWith(NV);
1199 NV->takeName(PN);
1200
1201 BB->getInstList().erase(PN);
1202 }
1203 return true;
1204}
1205
1206/// isTerminatorFirstRelevantInsn - Return true if Term is very first
1207/// instruction ignoring Phi nodes and dbg intrinsics.
1208static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1209 BasicBlock::iterator BBI = Term;
1210 while (BBI != BB->begin()) {
1211 --BBI;
1212 if (!isa<DbgInfoIntrinsic>(BBI))
1213 break;
1214 }
1215
1216 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1217 return true;
1218 return false;
1219}
1220
1221/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1222/// to two returning blocks, try to merge them together into one return,
1223/// introducing a select if the return values disagree.
1224static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1225 assert(BI->isConditional() && "Must be a conditional branch");
1226 BasicBlock *TrueSucc = BI->getSuccessor(0);
1227 BasicBlock *FalseSucc = BI->getSuccessor(1);
1228 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1229 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1230
1231 // Check to ensure both blocks are empty (just a return) or optionally empty
1232 // with PHI nodes. If there are other instructions, merging would cause extra
1233 // computation on one path or the other.
1234 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1235 return false;
1236 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1237 return false;
1238
1239 // Okay, we found a branch that is going to two return nodes. If
1240 // there is no return value for this function, just change the
1241 // branch into a return.
1242 if (FalseRet->getNumOperands() == 0) {
1243 TrueSucc->removePredecessor(BI->getParent());
1244 FalseSucc->removePredecessor(BI->getParent());
1245 ReturnInst::Create(BI->getContext(), 0, BI);
1246 EraseTerminatorInstAndDCECond(BI);
1247 return true;
1248 }
1249
1250 // Otherwise, figure out what the true and false return values are
1251 // so we can insert a new select instruction.
1252 Value *TrueValue = TrueRet->getReturnValue();
1253 Value *FalseValue = FalseRet->getReturnValue();
1254
1255 // Unwrap any PHI nodes in the return blocks.
1256 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1257 if (TVPN->getParent() == TrueSucc)
1258 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1259 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1260 if (FVPN->getParent() == FalseSucc)
1261 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1262
1263 // In order for this transformation to be safe, we must be able to
1264 // unconditionally execute both operands to the return. This is
1265 // normally the case, but we could have a potentially-trapping
1266 // constant expression that prevents this transformation from being
1267 // safe.
1268 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1269 if (TCV->canTrap())
1270 return false;
1271 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1272 if (FCV->canTrap())
1273 return false;
1274
1275 // Okay, we collected all the mapped values and checked them for sanity, and
1276 // defined to really do this transformation. First, update the CFG.
1277 TrueSucc->removePredecessor(BI->getParent());
1278 FalseSucc->removePredecessor(BI->getParent());
1279
1280 // Insert select instructions where needed.
1281 Value *BrCond = BI->getCondition();
1282 if (TrueValue) {
1283 // Insert a select if the results differ.
1284 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1285 } else if (isa<UndefValue>(TrueValue)) {
1286 TrueValue = FalseValue;
1287 } else {
1288 TrueValue = SelectInst::Create(BrCond, TrueValue,
1289 FalseValue, "retval", BI);
1290 }
1291 }
1292
1293 Value *RI = !TrueValue ?
1294 ReturnInst::Create(BI->getContext(), BI) :
1295 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1296 (void) RI;
1297
1298 DEBUG(errs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1299 << "\n " << *BI << "NewRet = " << *RI
1300 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1301
1302 EraseTerminatorInstAndDCECond(BI);
1303
1304 return true;
1305}
1306
1307/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1308/// and if a predecessor branches to us and one of our successors, fold the
1309/// setcc into the predecessor and use logical operations to pick the right
1310/// destination.
1311bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1312 BasicBlock *BB = BI->getParent();
1313 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1314 if (Cond == 0) return false;
1315
1316
1317 // Only allow this if the condition is a simple instruction that can be
1318 // executed unconditionally. It must be in the same block as the branch, and
1319 // must be at the front of the block.
1320 BasicBlock::iterator FrontIt = BB->front();
1321 // Ignore dbg intrinsics.
1322 while(isa<DbgInfoIntrinsic>(FrontIt))
1323 ++FrontIt;
1324 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1325 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1326 return false;
1327 }
1328
1329 // Make sure the instruction after the condition is the cond branch.
1330 BasicBlock::iterator CondIt = Cond; ++CondIt;
1331 // Ingore dbg intrinsics.
1332 while(isa<DbgInfoIntrinsic>(CondIt))
1333 ++CondIt;
1334 if (&*CondIt != BI) {
1335 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1336 return false;
1337 }
1338
1339 // Cond is known to be a compare or binary operator. Check to make sure that
1340 // neither operand is a potentially-trapping constant expression.
1341 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1342 if (CE->canTrap())
1343 return false;
1344 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1345 if (CE->canTrap())
1346 return false;
1347
1348
1349 // Finally, don't infinitely unroll conditional loops.
1350 BasicBlock *TrueDest = BI->getSuccessor(0);
1351 BasicBlock *FalseDest = BI->getSuccessor(1);
1352 if (TrueDest == BB || FalseDest == BB)
1353 return false;
1354
1355 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1356 BasicBlock *PredBlock = *PI;
1357 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1358
1359 // Check that we have two conditional branches. If there is a PHI node in
1360 // the common successor, verify that the same value flows in from both
1361 // blocks.
1362 if (PBI == 0 || PBI->isUnconditional() ||
1363 !SafeToMergeTerminators(BI, PBI))
1364 continue;
1365
1366 Instruction::BinaryOps Opc;
1367 bool InvertPredCond = false;
1368
1369 if (PBI->getSuccessor(0) == TrueDest)
1370 Opc = Instruction::Or;
1371 else if (PBI->getSuccessor(1) == FalseDest)
1372 Opc = Instruction::And;
1373 else if (PBI->getSuccessor(0) == FalseDest)
1374 Opc = Instruction::And, InvertPredCond = true;
1375 else if (PBI->getSuccessor(1) == TrueDest)
1376 Opc = Instruction::Or, InvertPredCond = true;
1377 else
1378 continue;
1379
1380 DEBUG(errs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1381
1382 // If we need to invert the condition in the pred block to match, do so now.
1383 if (InvertPredCond) {
1384 Value *NewCond =
1385 BinaryOperator::CreateNot(PBI->getCondition(),
1386 PBI->getCondition()->getName()+".not", PBI);
1387 PBI->setCondition(NewCond);
1388 BasicBlock *OldTrue = PBI->getSuccessor(0);
1389 BasicBlock *OldFalse = PBI->getSuccessor(1);
1390 PBI->setSuccessor(0, OldFalse);
1391 PBI->setSuccessor(1, OldTrue);
1392 }
1393
1394 // Clone Cond into the predecessor basic block, and or/and the
1395 // two conditions together.
1396 Instruction *New = Cond->clone();
1397 PredBlock->getInstList().insert(PBI, New);
1398 New->takeName(Cond);
1399 Cond->setName(New->getName()+".old");
1400
1401 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1402 New, "or.cond", PBI);
1403 PBI->setCondition(NewCond);
1404 if (PBI->getSuccessor(0) == BB) {
1405 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1406 PBI->setSuccessor(0, TrueDest);
1407 }
1408 if (PBI->getSuccessor(1) == BB) {
1409 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1410 PBI->setSuccessor(1, FalseDest);
1411 }
1412 return true;
1413 }
1414 return false;
1415}
1416
1417/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1418/// predecessor of another block, this function tries to simplify it. We know
1419/// that PBI and BI are both conditional branches, and BI is in one of the
1420/// successor blocks of PBI - PBI branches to BI.
1421static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1422 assert(PBI->isConditional() && BI->isConditional());
1423 BasicBlock *BB = BI->getParent();
1424
1425 // If this block ends with a branch instruction, and if there is a
1426 // predecessor that ends on a branch of the same condition, make
1427 // this conditional branch redundant.
1428 if (PBI->getCondition() == BI->getCondition() &&
1429 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1430 // Okay, the outcome of this conditional branch is statically
1431 // knowable. If this block had a single pred, handle specially.
1432 if (BB->getSinglePredecessor()) {
1433 // Turn this into a branch on constant.
1434 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1435 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1436 CondIsTrue));
1437 return true; // Nuke the branch on constant.
1438 }
1439
1440 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1441 // in the constant and simplify the block result. Subsequent passes of
1442 // simplifycfg will thread the block.
1443 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1444 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1445 BI->getCondition()->getName() + ".pr",
1446 BB->begin());
1447 // Okay, we're going to insert the PHI node. Since PBI is not the only
1448 // predecessor, compute the PHI'd conditional value for all of the preds.
1449 // Any predecessor where the condition is not computable we keep symbolic.
1450 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1451 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1452 PBI != BI && PBI->isConditional() &&
1453 PBI->getCondition() == BI->getCondition() &&
1454 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1455 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1456 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1457 CondIsTrue), *PI);
1458 } else {
1459 NewPN->addIncoming(BI->getCondition(), *PI);
1460 }
1461
1462 BI->setCondition(NewPN);
1463 return true;
1464 }
1465 }
1466
1467 // If this is a conditional branch in an empty block, and if any
1468 // predecessors is a conditional branch to one of our destinations,
1469 // fold the conditions into logical ops and one cond br.
1470 BasicBlock::iterator BBI = BB->begin();
1471 // Ignore dbg intrinsics.
1472 while (isa<DbgInfoIntrinsic>(BBI))
1473 ++BBI;
1474 if (&*BBI != BI)
1475 return false;
1476
1477
1478 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1479 if (CE->canTrap())
1480 return false;
1481
1482 int PBIOp, BIOp;
1483 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1484 PBIOp = BIOp = 0;
1485 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1486 PBIOp = 0, BIOp = 1;
1487 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1488 PBIOp = 1, BIOp = 0;
1489 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1490 PBIOp = BIOp = 1;
1491 else
1492 return false;
1493
1494 // Check to make sure that the other destination of this branch
1495 // isn't BB itself. If so, this is an infinite loop that will
1496 // keep getting unwound.
1497 if (PBI->getSuccessor(PBIOp) == BB)
1498 return false;
1499
1500 // Do not perform this transformation if it would require
1501 // insertion of a large number of select instructions. For targets
1502 // without predication/cmovs, this is a big pessimization.
1503 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1504
1505 unsigned NumPhis = 0;
1506 for (BasicBlock::iterator II = CommonDest->begin();
1507 isa<PHINode>(II); ++II, ++NumPhis)
1508 if (NumPhis > 2) // Disable this xform.
1509 return false;
1510
1511 // Finally, if everything is ok, fold the branches to logical ops.
1512 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1513
1514 DEBUG(errs() << "FOLDING BRs:" << *PBI->getParent()
1515 << "AND: " << *BI->getParent());
1516
1517
1518 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1519 // branch in it, where one edge (OtherDest) goes back to itself but the other
1520 // exits. We don't *know* that the program avoids the infinite loop
1521 // (even though that seems likely). If we do this xform naively, we'll end up
1522 // recursively unpeeling the loop. Since we know that (after the xform is
1523 // done) that the block *is* infinite if reached, we just make it an obviously
1524 // infinite loop with no cond branch.
1525 if (OtherDest == BB) {
1526 // Insert it at the end of the function, because it's either code,
1527 // or it won't matter if it's hot. :)
1528 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1529 "infloop", BB->getParent());
1530 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1531 OtherDest = InfLoopBlock;
1532 }
1533
1534 DEBUG(errs() << *PBI->getParent()->getParent());
1535
1536 // BI may have other predecessors. Because of this, we leave
1537 // it alone, but modify PBI.
1538
1539 // Make sure we get to CommonDest on True&True directions.
1540 Value *PBICond = PBI->getCondition();
1541 if (PBIOp)
1542 PBICond = BinaryOperator::CreateNot(PBICond,
1543 PBICond->getName()+".not",
1544 PBI);
1545 Value *BICond = BI->getCondition();
1546 if (BIOp)
1547 BICond = BinaryOperator::CreateNot(BICond,
1548 BICond->getName()+".not",
1549 PBI);
1550 // Merge the conditions.
1551 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1552
1553 // Modify PBI to branch on the new condition to the new dests.
1554 PBI->setCondition(Cond);
1555 PBI->setSuccessor(0, CommonDest);
1556 PBI->setSuccessor(1, OtherDest);
1557
1558 // OtherDest may have phi nodes. If so, add an entry from PBI's
1559 // block that are identical to the entries for BI's block.
1560 PHINode *PN;
1561 for (BasicBlock::iterator II = OtherDest->begin();
1562 (PN = dyn_cast<PHINode>(II)); ++II) {
1563 Value *V = PN->getIncomingValueForBlock(BB);
1564 PN->addIncoming(V, PBI->getParent());
1565 }
1566
1567 // We know that the CommonDest already had an edge from PBI to
1568 // it. If it has PHIs though, the PHIs may have different
1569 // entries for BB and PBI's BB. If so, insert a select to make
1570 // them agree.
1571 for (BasicBlock::iterator II = CommonDest->begin();
1572 (PN = dyn_cast<PHINode>(II)); ++II) {
1573 Value *BIV = PN->getIncomingValueForBlock(BB);
1574 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1575 Value *PBIV = PN->getIncomingValue(PBBIdx);
1576 if (BIV != PBIV) {
1577 // Insert a select in PBI to pick the right value.
1578 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1579 PBIV->getName()+".mux", PBI);
1580 PN->setIncomingValue(PBBIdx, NV);
1581 }
1582 }
1583
1584 DEBUG(errs() << "INTO: " << *PBI->getParent());
1585 DEBUG(errs() << *PBI->getParent()->getParent());
1586
1587 // This basic block is probably dead. We know it has at least
1588 // one fewer predecessor.
1589 return true;
1590}
1591
1592/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
1593/// nodes in this block. This doesn't try to be clever about PHI nodes
1594/// which differ only in the order of the incoming values, but instcombine
1595/// orders them so it usually won't matter.
1596///
| 1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Peephole optimize the CFG.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "simplifycfg"
15#include "llvm/Transforms/Utils/Local.h"
16#include "llvm/Constants.h"
17#include "llvm/Instructions.h"
18#include "llvm/IntrinsicInst.h"
19#include "llvm/Type.h"
20#include "llvm/DerivedTypes.h"
21#include "llvm/GlobalVariable.h"
22#include "llvm/Support/CFG.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/Support/raw_ostream.h"
25#include "llvm/Analysis/ConstantFolding.h"
26#include "llvm/Transforms/Utils/BasicBlockUtils.h"
27#include "llvm/ADT/DenseMap.h"
28#include "llvm/ADT/SmallVector.h"
29#include "llvm/ADT/SmallPtrSet.h"
30#include "llvm/ADT/Statistic.h"
31#include <algorithm>
32#include <functional>
33#include <set>
34#include <map>
35using namespace llvm;
36
37STATISTIC(NumSpeculations, "Number of speculative executed instructions");
38
39/// SafeToMergeTerminators - Return true if it is safe to merge these two
40/// terminator instructions together.
41///
42static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
43 if (SI1 == SI2) return false; // Can't merge with self!
44
45 // It is not safe to merge these two switch instructions if they have a common
46 // successor, and if that successor has a PHI node, and if *that* PHI node has
47 // conflicting incoming values from the two switch blocks.
48 BasicBlock *SI1BB = SI1->getParent();
49 BasicBlock *SI2BB = SI2->getParent();
50 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
51
52 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
53 if (SI1Succs.count(*I))
54 for (BasicBlock::iterator BBI = (*I)->begin();
55 isa<PHINode>(BBI); ++BBI) {
56 PHINode *PN = cast<PHINode>(BBI);
57 if (PN->getIncomingValueForBlock(SI1BB) !=
58 PN->getIncomingValueForBlock(SI2BB))
59 return false;
60 }
61
62 return true;
63}
64
65/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
66/// now be entries in it from the 'NewPred' block. The values that will be
67/// flowing into the PHI nodes will be the same as those coming in from
68/// ExistPred, an existing predecessor of Succ.
69static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
70 BasicBlock *ExistPred) {
71 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
72 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
73 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
74
75 PHINode *PN;
76 for (BasicBlock::iterator I = Succ->begin();
77 (PN = dyn_cast<PHINode>(I)); ++I)
78 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
79}
80
81
82/// GetIfCondition - Given a basic block (BB) with two predecessors (and
83/// presumably PHI nodes in it), check to see if the merge at this block is due
84/// to an "if condition". If so, return the boolean condition that determines
85/// which entry into BB will be taken. Also, return by references the block
86/// that will be entered from if the condition is true, and the block that will
87/// be entered if the condition is false.
88///
89///
90static Value *GetIfCondition(BasicBlock *BB,
91 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
92 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
93 "Function can only handle blocks with 2 predecessors!");
94 BasicBlock *Pred1 = *pred_begin(BB);
95 BasicBlock *Pred2 = *++pred_begin(BB);
96
97 // We can only handle branches. Other control flow will be lowered to
98 // branches if possible anyway.
99 if (!isa<BranchInst>(Pred1->getTerminator()) ||
100 !isa<BranchInst>(Pred2->getTerminator()))
101 return 0;
102 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
103 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
104
105 // Eliminate code duplication by ensuring that Pred1Br is conditional if
106 // either are.
107 if (Pred2Br->isConditional()) {
108 // If both branches are conditional, we don't have an "if statement". In
109 // reality, we could transform this case, but since the condition will be
110 // required anyway, we stand no chance of eliminating it, so the xform is
111 // probably not profitable.
112 if (Pred1Br->isConditional())
113 return 0;
114
115 std::swap(Pred1, Pred2);
116 std::swap(Pred1Br, Pred2Br);
117 }
118
119 if (Pred1Br->isConditional()) {
120 // If we found a conditional branch predecessor, make sure that it branches
121 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
122 if (Pred1Br->getSuccessor(0) == BB &&
123 Pred1Br->getSuccessor(1) == Pred2) {
124 IfTrue = Pred1;
125 IfFalse = Pred2;
126 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
127 Pred1Br->getSuccessor(1) == BB) {
128 IfTrue = Pred2;
129 IfFalse = Pred1;
130 } else {
131 // We know that one arm of the conditional goes to BB, so the other must
132 // go somewhere unrelated, and this must not be an "if statement".
133 return 0;
134 }
135
136 // The only thing we have to watch out for here is to make sure that Pred2
137 // doesn't have incoming edges from other blocks. If it does, the condition
138 // doesn't dominate BB.
139 if (++pred_begin(Pred2) != pred_end(Pred2))
140 return 0;
141
142 return Pred1Br->getCondition();
143 }
144
145 // Ok, if we got here, both predecessors end with an unconditional branch to
146 // BB. Don't panic! If both blocks only have a single (identical)
147 // predecessor, and THAT is a conditional branch, then we're all ok!
148 if (pred_begin(Pred1) == pred_end(Pred1) ||
149 ++pred_begin(Pred1) != pred_end(Pred1) ||
150 pred_begin(Pred2) == pred_end(Pred2) ||
151 ++pred_begin(Pred2) != pred_end(Pred2) ||
152 *pred_begin(Pred1) != *pred_begin(Pred2))
153 return 0;
154
155 // Otherwise, if this is a conditional branch, then we can use it!
156 BasicBlock *CommonPred = *pred_begin(Pred1);
157 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
158 assert(BI->isConditional() && "Two successors but not conditional?");
159 if (BI->getSuccessor(0) == Pred1) {
160 IfTrue = Pred1;
161 IfFalse = Pred2;
162 } else {
163 IfTrue = Pred2;
164 IfFalse = Pred1;
165 }
166 return BI->getCondition();
167 }
168 return 0;
169}
170
171/// DominatesMergePoint - If we have a merge point of an "if condition" as
172/// accepted above, return true if the specified value dominates the block. We
173/// don't handle the true generality of domination here, just a special case
174/// which works well enough for us.
175///
176/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
177/// see if V (which must be an instruction) is cheap to compute and is
178/// non-trapping. If both are true, the instruction is inserted into the set
179/// and true is returned.
180static bool DominatesMergePoint(Value *V, BasicBlock *BB,
181 std::set<Instruction*> *AggressiveInsts) {
182 Instruction *I = dyn_cast<Instruction>(V);
183 if (!I) {
184 // Non-instructions all dominate instructions, but not all constantexprs
185 // can be executed unconditionally.
186 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
187 if (C->canTrap())
188 return false;
189 return true;
190 }
191 BasicBlock *PBB = I->getParent();
192
193 // We don't want to allow weird loops that might have the "if condition" in
194 // the bottom of this block.
195 if (PBB == BB) return false;
196
197 // If this instruction is defined in a block that contains an unconditional
198 // branch to BB, then it must be in the 'conditional' part of the "if
199 // statement".
200 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
201 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
202 if (!AggressiveInsts) return false;
203 // Okay, it looks like the instruction IS in the "condition". Check to
204 // see if its a cheap instruction to unconditionally compute, and if it
205 // only uses stuff defined outside of the condition. If so, hoist it out.
206 if (!I->isSafeToSpeculativelyExecute())
207 return false;
208
209 switch (I->getOpcode()) {
210 default: return false; // Cannot hoist this out safely.
211 case Instruction::Load: {
212 // We have to check to make sure there are no instructions before the
213 // load in its basic block, as we are going to hoist the loop out to
214 // its predecessor.
215 BasicBlock::iterator IP = PBB->begin();
216 while (isa<DbgInfoIntrinsic>(IP))
217 IP++;
218 if (IP != BasicBlock::iterator(I))
219 return false;
220 break;
221 }
222 case Instruction::Add:
223 case Instruction::Sub:
224 case Instruction::And:
225 case Instruction::Or:
226 case Instruction::Xor:
227 case Instruction::Shl:
228 case Instruction::LShr:
229 case Instruction::AShr:
230 case Instruction::ICmp:
231 break; // These are all cheap and non-trapping instructions.
232 }
233
234 // Okay, we can only really hoist these out if their operands are not
235 // defined in the conditional region.
236 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
237 if (!DominatesMergePoint(*i, BB, 0))
238 return false;
239 // Okay, it's safe to do this! Remember this instruction.
240 AggressiveInsts->insert(I);
241 }
242
243 return true;
244}
245
246/// GatherConstantSetEQs - Given a potentially 'or'd together collection of
247/// icmp_eq instructions that compare a value against a constant, return the
248/// value being compared, and stick the constant into the Values vector.
249static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
250 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
251 if (Inst->getOpcode() == Instruction::ICmp &&
252 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
253 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
254 Values.push_back(C);
255 return Inst->getOperand(0);
256 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
257 Values.push_back(C);
258 return Inst->getOperand(1);
259 }
260 } else if (Inst->getOpcode() == Instruction::Or) {
261 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
262 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
263 if (LHS == RHS)
264 return LHS;
265 }
266 }
267 return 0;
268}
269
270/// GatherConstantSetNEs - Given a potentially 'and'd together collection of
271/// setne instructions that compare a value against a constant, return the value
272/// being compared, and stick the constant into the Values vector.
273static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
274 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
275 if (Inst->getOpcode() == Instruction::ICmp &&
276 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
277 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
278 Values.push_back(C);
279 return Inst->getOperand(0);
280 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
281 Values.push_back(C);
282 return Inst->getOperand(1);
283 }
284 } else if (Inst->getOpcode() == Instruction::And) {
285 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
286 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
287 if (LHS == RHS)
288 return LHS;
289 }
290 }
291 return 0;
292}
293
294/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
295/// bunch of comparisons of one value against constants, return the value and
296/// the constants being compared.
297static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
298 std::vector<ConstantInt*> &Values) {
299 if (Cond->getOpcode() == Instruction::Or) {
300 CompVal = GatherConstantSetEQs(Cond, Values);
301
302 // Return true to indicate that the condition is true if the CompVal is
303 // equal to one of the constants.
304 return true;
305 } else if (Cond->getOpcode() == Instruction::And) {
306 CompVal = GatherConstantSetNEs(Cond, Values);
307
308 // Return false to indicate that the condition is false if the CompVal is
309 // equal to one of the constants.
310 return false;
311 }
312 return false;
313}
314
315static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
316 Instruction* Cond = 0;
317 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
318 Cond = dyn_cast<Instruction>(SI->getCondition());
319 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
320 if (BI->isConditional())
321 Cond = dyn_cast<Instruction>(BI->getCondition());
322 }
323
324 TI->eraseFromParent();
325 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
326}
327
328/// isValueEqualityComparison - Return true if the specified terminator checks
329/// to see if a value is equal to constant integer value.
330static Value *isValueEqualityComparison(TerminatorInst *TI) {
331 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
332 // Do not permit merging of large switch instructions into their
333 // predecessors unless there is only one predecessor.
334 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
335 pred_end(SI->getParent())) > 128)
336 return 0;
337
338 return SI->getCondition();
339 }
340 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
341 if (BI->isConditional() && BI->getCondition()->hasOneUse())
342 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
343 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
344 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
345 isa<ConstantInt>(ICI->getOperand(1)))
346 return ICI->getOperand(0);
347 return 0;
348}
349
350/// GetValueEqualityComparisonCases - Given a value comparison instruction,
351/// decode all of the 'cases' that it represents and return the 'default' block.
352static BasicBlock *
353GetValueEqualityComparisonCases(TerminatorInst *TI,
354 std::vector<std::pair<ConstantInt*,
355 BasicBlock*> > &Cases) {
356 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
357 Cases.reserve(SI->getNumCases());
358 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
359 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
360 return SI->getDefaultDest();
361 }
362
363 BranchInst *BI = cast<BranchInst>(TI);
364 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
365 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
366 BI->getSuccessor(ICI->getPredicate() ==
367 ICmpInst::ICMP_NE)));
368 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
369}
370
371
372/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
373/// in the list that match the specified block.
374static void EliminateBlockCases(BasicBlock *BB,
375 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
376 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
377 if (Cases[i].second == BB) {
378 Cases.erase(Cases.begin()+i);
379 --i; --e;
380 }
381}
382
383/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
384/// well.
385static bool
386ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
387 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
388 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
389
390 // Make V1 be smaller than V2.
391 if (V1->size() > V2->size())
392 std::swap(V1, V2);
393
394 if (V1->size() == 0) return false;
395 if (V1->size() == 1) {
396 // Just scan V2.
397 ConstantInt *TheVal = (*V1)[0].first;
398 for (unsigned i = 0, e = V2->size(); i != e; ++i)
399 if (TheVal == (*V2)[i].first)
400 return true;
401 }
402
403 // Otherwise, just sort both lists and compare element by element.
404 std::sort(V1->begin(), V1->end());
405 std::sort(V2->begin(), V2->end());
406 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
407 while (i1 != e1 && i2 != e2) {
408 if ((*V1)[i1].first == (*V2)[i2].first)
409 return true;
410 if ((*V1)[i1].first < (*V2)[i2].first)
411 ++i1;
412 else
413 ++i2;
414 }
415 return false;
416}
417
418/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
419/// terminator instruction and its block is known to only have a single
420/// predecessor block, check to see if that predecessor is also a value
421/// comparison with the same value, and if that comparison determines the
422/// outcome of this comparison. If so, simplify TI. This does a very limited
423/// form of jump threading.
424static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
425 BasicBlock *Pred) {
426 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
427 if (!PredVal) return false; // Not a value comparison in predecessor.
428
429 Value *ThisVal = isValueEqualityComparison(TI);
430 assert(ThisVal && "This isn't a value comparison!!");
431 if (ThisVal != PredVal) return false; // Different predicates.
432
433 // Find out information about when control will move from Pred to TI's block.
434 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
435 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
436 PredCases);
437 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
438
439 // Find information about how control leaves this block.
440 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
441 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
442 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
443
444 // If TI's block is the default block from Pred's comparison, potentially
445 // simplify TI based on this knowledge.
446 if (PredDef == TI->getParent()) {
447 // If we are here, we know that the value is none of those cases listed in
448 // PredCases. If there are any cases in ThisCases that are in PredCases, we
449 // can simplify TI.
450 if (ValuesOverlap(PredCases, ThisCases)) {
451 if (isa<BranchInst>(TI)) {
452 // Okay, one of the successors of this condbr is dead. Convert it to a
453 // uncond br.
454 assert(ThisCases.size() == 1 && "Branch can only have one case!");
455 // Insert the new branch.
456 Instruction *NI = BranchInst::Create(ThisDef, TI);
457 (void) NI;
458
459 // Remove PHI node entries for the dead edge.
460 ThisCases[0].second->removePredecessor(TI->getParent());
461
462 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
463 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
464
465 EraseTerminatorInstAndDCECond(TI);
466 return true;
467
468 } else {
469 SwitchInst *SI = cast<SwitchInst>(TI);
470 // Okay, TI has cases that are statically dead, prune them away.
471 SmallPtrSet<Constant*, 16> DeadCases;
472 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
473 DeadCases.insert(PredCases[i].first);
474
475 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
476 << "Through successor TI: " << *TI);
477
478 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
479 if (DeadCases.count(SI->getCaseValue(i))) {
480 SI->getSuccessor(i)->removePredecessor(TI->getParent());
481 SI->removeCase(i);
482 }
483
484 DEBUG(errs() << "Leaving: " << *TI << "\n");
485 return true;
486 }
487 }
488
489 } else {
490 // Otherwise, TI's block must correspond to some matched value. Find out
491 // which value (or set of values) this is.
492 ConstantInt *TIV = 0;
493 BasicBlock *TIBB = TI->getParent();
494 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
495 if (PredCases[i].second == TIBB) {
496 if (TIV == 0)
497 TIV = PredCases[i].first;
498 else
499 return false; // Cannot handle multiple values coming to this block.
500 }
501 assert(TIV && "No edge from pred to succ?");
502
503 // Okay, we found the one constant that our value can be if we get into TI's
504 // BB. Find out which successor will unconditionally be branched to.
505 BasicBlock *TheRealDest = 0;
506 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
507 if (ThisCases[i].first == TIV) {
508 TheRealDest = ThisCases[i].second;
509 break;
510 }
511
512 // If not handled by any explicit cases, it is handled by the default case.
513 if (TheRealDest == 0) TheRealDest = ThisDef;
514
515 // Remove PHI node entries for dead edges.
516 BasicBlock *CheckEdge = TheRealDest;
517 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
518 if (*SI != CheckEdge)
519 (*SI)->removePredecessor(TIBB);
520 else
521 CheckEdge = 0;
522
523 // Insert the new branch.
524 Instruction *NI = BranchInst::Create(TheRealDest, TI);
525 (void) NI;
526
527 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
528 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
529
530 EraseTerminatorInstAndDCECond(TI);
531 return true;
532 }
533 return false;
534}
535
536namespace {
537 /// ConstantIntOrdering - This class implements a stable ordering of constant
538 /// integers that does not depend on their address. This is important for
539 /// applications that sort ConstantInt's to ensure uniqueness.
540 struct ConstantIntOrdering {
541 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
542 return LHS->getValue().ult(RHS->getValue());
543 }
544 };
545}
546
547/// FoldValueComparisonIntoPredecessors - The specified terminator is a value
548/// equality comparison instruction (either a switch or a branch on "X == c").
549/// See if any of the predecessors of the terminator block are value comparisons
550/// on the same value. If so, and if safe to do so, fold them together.
551static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
552 BasicBlock *BB = TI->getParent();
553 Value *CV = isValueEqualityComparison(TI); // CondVal
554 assert(CV && "Not a comparison?");
555 bool Changed = false;
556
557 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
558 while (!Preds.empty()) {
559 BasicBlock *Pred = Preds.pop_back_val();
560
561 // See if the predecessor is a comparison with the same value.
562 TerminatorInst *PTI = Pred->getTerminator();
563 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
564
565 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
566 // Figure out which 'cases' to copy from SI to PSI.
567 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
568 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
569
570 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
571 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
572
573 // Based on whether the default edge from PTI goes to BB or not, fill in
574 // PredCases and PredDefault with the new switch cases we would like to
575 // build.
576 SmallVector<BasicBlock*, 8> NewSuccessors;
577
578 if (PredDefault == BB) {
579 // If this is the default destination from PTI, only the edges in TI
580 // that don't occur in PTI, or that branch to BB will be activated.
581 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
582 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
583 if (PredCases[i].second != BB)
584 PTIHandled.insert(PredCases[i].first);
585 else {
586 // The default destination is BB, we don't need explicit targets.
587 std::swap(PredCases[i], PredCases.back());
588 PredCases.pop_back();
589 --i; --e;
590 }
591
592 // Reconstruct the new switch statement we will be building.
593 if (PredDefault != BBDefault) {
594 PredDefault->removePredecessor(Pred);
595 PredDefault = BBDefault;
596 NewSuccessors.push_back(BBDefault);
597 }
598 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
599 if (!PTIHandled.count(BBCases[i].first) &&
600 BBCases[i].second != BBDefault) {
601 PredCases.push_back(BBCases[i]);
602 NewSuccessors.push_back(BBCases[i].second);
603 }
604
605 } else {
606 // If this is not the default destination from PSI, only the edges
607 // in SI that occur in PSI with a destination of BB will be
608 // activated.
609 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
610 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
611 if (PredCases[i].second == BB) {
612 PTIHandled.insert(PredCases[i].first);
613 std::swap(PredCases[i], PredCases.back());
614 PredCases.pop_back();
615 --i; --e;
616 }
617
618 // Okay, now we know which constants were sent to BB from the
619 // predecessor. Figure out where they will all go now.
620 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
621 if (PTIHandled.count(BBCases[i].first)) {
622 // If this is one we are capable of getting...
623 PredCases.push_back(BBCases[i]);
624 NewSuccessors.push_back(BBCases[i].second);
625 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
626 }
627
628 // If there are any constants vectored to BB that TI doesn't handle,
629 // they must go to the default destination of TI.
630 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
631 PTIHandled.begin(),
632 E = PTIHandled.end(); I != E; ++I) {
633 PredCases.push_back(std::make_pair(*I, BBDefault));
634 NewSuccessors.push_back(BBDefault);
635 }
636 }
637
638 // Okay, at this point, we know which new successor Pred will get. Make
639 // sure we update the number of entries in the PHI nodes for these
640 // successors.
641 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
642 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
643
644 // Now that the successors are updated, create the new Switch instruction.
645 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
646 PredCases.size(), PTI);
647 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
648 NewSI->addCase(PredCases[i].first, PredCases[i].second);
649
650 EraseTerminatorInstAndDCECond(PTI);
651
652 // Okay, last check. If BB is still a successor of PSI, then we must
653 // have an infinite loop case. If so, add an infinitely looping block
654 // to handle the case to preserve the behavior of the code.
655 BasicBlock *InfLoopBlock = 0;
656 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
657 if (NewSI->getSuccessor(i) == BB) {
658 if (InfLoopBlock == 0) {
659 // Insert it at the end of the function, because it's either code,
660 // or it won't matter if it's hot. :)
661 InfLoopBlock = BasicBlock::Create(BB->getContext(),
662 "infloop", BB->getParent());
663 BranchInst::Create(InfLoopBlock, InfLoopBlock);
664 }
665 NewSI->setSuccessor(i, InfLoopBlock);
666 }
667
668 Changed = true;
669 }
670 }
671 return Changed;
672}
673
674// isSafeToHoistInvoke - If we would need to insert a select that uses the
675// value of this invoke (comments in HoistThenElseCodeToIf explain why we
676// would need to do this), we can't hoist the invoke, as there is nowhere
677// to put the select in this case.
678static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
679 Instruction *I1, Instruction *I2) {
680 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
681 PHINode *PN;
682 for (BasicBlock::iterator BBI = SI->begin();
683 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
684 Value *BB1V = PN->getIncomingValueForBlock(BB1);
685 Value *BB2V = PN->getIncomingValueForBlock(BB2);
686 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
687 return false;
688 }
689 }
690 }
691 return true;
692}
693
694/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
695/// BB2, hoist any common code in the two blocks up into the branch block. The
696/// caller of this function guarantees that BI's block dominates BB1 and BB2.
697static bool HoistThenElseCodeToIf(BranchInst *BI) {
698 // This does very trivial matching, with limited scanning, to find identical
699 // instructions in the two blocks. In particular, we don't want to get into
700 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
701 // such, we currently just scan for obviously identical instructions in an
702 // identical order.
703 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
704 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
705
706 BasicBlock::iterator BB1_Itr = BB1->begin();
707 BasicBlock::iterator BB2_Itr = BB2->begin();
708
709 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
710 while (isa<DbgInfoIntrinsic>(I1))
711 I1 = BB1_Itr++;
712 while (isa<DbgInfoIntrinsic>(I2))
713 I2 = BB2_Itr++;
714 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
715 !I1->isIdenticalToWhenDefined(I2) ||
716 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
717 return false;
718
719 // If we get here, we can hoist at least one instruction.
720 BasicBlock *BIParent = BI->getParent();
721
722 do {
723 // If we are hoisting the terminator instruction, don't move one (making a
724 // broken BB), instead clone it, and remove BI.
725 if (isa<TerminatorInst>(I1))
726 goto HoistTerminator;
727
728 // For a normal instruction, we just move one to right before the branch,
729 // then replace all uses of the other with the first. Finally, we remove
730 // the now redundant second instruction.
731 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
732 if (!I2->use_empty())
733 I2->replaceAllUsesWith(I1);
734 I1->intersectOptionalDataWith(I2);
735 BB2->getInstList().erase(I2);
736
737 I1 = BB1_Itr++;
738 while (isa<DbgInfoIntrinsic>(I1))
739 I1 = BB1_Itr++;
740 I2 = BB2_Itr++;
741 while (isa<DbgInfoIntrinsic>(I2))
742 I2 = BB2_Itr++;
743 } while (I1->getOpcode() == I2->getOpcode() &&
744 I1->isIdenticalToWhenDefined(I2));
745
746 return true;
747
748HoistTerminator:
749 // It may not be possible to hoist an invoke.
750 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
751 return true;
752
753 // Okay, it is safe to hoist the terminator.
754 Instruction *NT = I1->clone();
755 BIParent->getInstList().insert(BI, NT);
756 if (NT->getType() != Type::getVoidTy(BB1->getContext())) {
757 I1->replaceAllUsesWith(NT);
758 I2->replaceAllUsesWith(NT);
759 NT->takeName(I1);
760 }
761
762 // Hoisting one of the terminators from our successor is a great thing.
763 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
764 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
765 // nodes, so we insert select instruction to compute the final result.
766 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
767 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
768 PHINode *PN;
769 for (BasicBlock::iterator BBI = SI->begin();
770 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
771 Value *BB1V = PN->getIncomingValueForBlock(BB1);
772 Value *BB2V = PN->getIncomingValueForBlock(BB2);
773 if (BB1V != BB2V) {
774 // These values do not agree. Insert a select instruction before NT
775 // that determines the right value.
776 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
777 if (SI == 0)
778 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
779 BB1V->getName()+"."+BB2V->getName(), NT);
780 // Make the PHI node use the select for all incoming values for BB1/BB2
781 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
782 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
783 PN->setIncomingValue(i, SI);
784 }
785 }
786 }
787
788 // Update any PHI nodes in our new successors.
789 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
790 AddPredecessorToBlock(*SI, BIParent, BB1);
791
792 EraseTerminatorInstAndDCECond(BI);
793 return true;
794}
795
796/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
797/// and an BB2 and the only successor of BB1 is BB2, hoist simple code
798/// (for now, restricted to a single instruction that's side effect free) from
799/// the BB1 into the branch block to speculatively execute it.
800static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
801 // Only speculatively execution a single instruction (not counting the
802 // terminator) for now.
803 Instruction *HInst = NULL;
804 Instruction *Term = BB1->getTerminator();
805 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
806 BBI != BBE; ++BBI) {
807 Instruction *I = BBI;
808 // Skip debug info.
809 if (isa<DbgInfoIntrinsic>(I)) continue;
810 if (I == Term) break;
811
812 if (!HInst)
813 HInst = I;
814 else
815 return false;
816 }
817 if (!HInst)
818 return false;
819
820 // Be conservative for now. FP select instruction can often be expensive.
821 Value *BrCond = BI->getCondition();
822 if (isa<Instruction>(BrCond) &&
823 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
824 return false;
825
826 // If BB1 is actually on the false edge of the conditional branch, remember
827 // to swap the select operands later.
828 bool Invert = false;
829 if (BB1 != BI->getSuccessor(0)) {
830 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
831 Invert = true;
832 }
833
834 // Turn
835 // BB:
836 // %t1 = icmp
837 // br i1 %t1, label %BB1, label %BB2
838 // BB1:
839 // %t3 = add %t2, c
840 // br label BB2
841 // BB2:
842 // =>
843 // BB:
844 // %t1 = icmp
845 // %t4 = add %t2, c
846 // %t3 = select i1 %t1, %t2, %t3
847 switch (HInst->getOpcode()) {
848 default: return false; // Not safe / profitable to hoist.
849 case Instruction::Add:
850 case Instruction::Sub:
851 // Not worth doing for vector ops.
852 if (isa<VectorType>(HInst->getType()))
853 return false;
854 break;
855 case Instruction::And:
856 case Instruction::Or:
857 case Instruction::Xor:
858 case Instruction::Shl:
859 case Instruction::LShr:
860 case Instruction::AShr:
861 // Don't mess with vector operations.
862 if (isa<VectorType>(HInst->getType()))
863 return false;
864 break; // These are all cheap and non-trapping instructions.
865 }
866
867 // If the instruction is obviously dead, don't try to predicate it.
868 if (HInst->use_empty()) {
869 HInst->eraseFromParent();
870 return true;
871 }
872
873 // Can we speculatively execute the instruction? And what is the value
874 // if the condition is false? Consider the phi uses, if the incoming value
875 // from the "if" block are all the same V, then V is the value of the
876 // select if the condition is false.
877 BasicBlock *BIParent = BI->getParent();
878 SmallVector<PHINode*, 4> PHIUses;
879 Value *FalseV = NULL;
880
881 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
882 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
883 UI != E; ++UI) {
884 // Ignore any user that is not a PHI node in BB2. These can only occur in
885 // unreachable blocks, because they would not be dominated by the instr.
886 PHINode *PN = dyn_cast<PHINode>(UI);
887 if (!PN || PN->getParent() != BB2)
888 return false;
889 PHIUses.push_back(PN);
890
891 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
892 if (!FalseV)
893 FalseV = PHIV;
894 else if (FalseV != PHIV)
895 return false; // Inconsistent value when condition is false.
896 }
897
898 assert(FalseV && "Must have at least one user, and it must be a PHI");
899
900 // Do not hoist the instruction if any of its operands are defined but not
901 // used in this BB. The transformation will prevent the operand from
902 // being sunk into the use block.
903 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
904 i != e; ++i) {
905 Instruction *OpI = dyn_cast<Instruction>(*i);
906 if (OpI && OpI->getParent() == BIParent &&
907 !OpI->isUsedInBasicBlock(BIParent))
908 return false;
909 }
910
911 // If we get here, we can hoist the instruction. Try to place it
912 // before the icmp instruction preceding the conditional branch.
913 BasicBlock::iterator InsertPos = BI;
914 if (InsertPos != BIParent->begin())
915 --InsertPos;
916 // Skip debug info between condition and branch.
917 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
918 --InsertPos;
919 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
920 SmallPtrSet<Instruction *, 4> BB1Insns;
921 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
922 BB1I != BB1E; ++BB1I)
923 BB1Insns.insert(BB1I);
924 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
925 UI != UE; ++UI) {
926 Instruction *Use = cast<Instruction>(*UI);
927 if (BB1Insns.count(Use)) {
928 // If BrCond uses the instruction that place it just before
929 // branch instruction.
930 InsertPos = BI;
931 break;
932 }
933 }
934 } else
935 InsertPos = BI;
936 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
937
938 // Create a select whose true value is the speculatively executed value and
939 // false value is the previously determined FalseV.
940 SelectInst *SI;
941 if (Invert)
942 SI = SelectInst::Create(BrCond, FalseV, HInst,
943 FalseV->getName() + "." + HInst->getName(), BI);
944 else
945 SI = SelectInst::Create(BrCond, HInst, FalseV,
946 HInst->getName() + "." + FalseV->getName(), BI);
947
948 // Make the PHI node use the select for all incoming values for "then" and
949 // "if" blocks.
950 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
951 PHINode *PN = PHIUses[i];
952 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
953 if (PN->getIncomingBlock(j) == BB1 ||
954 PN->getIncomingBlock(j) == BIParent)
955 PN->setIncomingValue(j, SI);
956 }
957
958 ++NumSpeculations;
959 return true;
960}
961
962/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
963/// across this block.
964static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
965 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
966 unsigned Size = 0;
967
968 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
969 if (isa<DbgInfoIntrinsic>(BBI))
970 continue;
971 if (Size > 10) return false; // Don't clone large BB's.
972 ++Size;
973
974 // We can only support instructions that do not define values that are
975 // live outside of the current basic block.
976 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
977 UI != E; ++UI) {
978 Instruction *U = cast<Instruction>(*UI);
979 if (U->getParent() != BB || isa<PHINode>(U)) return false;
980 }
981
982 // Looks ok, continue checking.
983 }
984
985 return true;
986}
987
988/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
989/// that is defined in the same block as the branch and if any PHI entries are
990/// constants, thread edges corresponding to that entry to be branches to their
991/// ultimate destination.
992static bool FoldCondBranchOnPHI(BranchInst *BI) {
993 BasicBlock *BB = BI->getParent();
994 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
995 // NOTE: we currently cannot transform this case if the PHI node is used
996 // outside of the block.
997 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
998 return false;
999
1000 // Degenerate case of a single entry PHI.
1001 if (PN->getNumIncomingValues() == 1) {
1002 FoldSingleEntryPHINodes(PN->getParent());
1003 return true;
1004 }
1005
1006 // Now we know that this block has multiple preds and two succs.
1007 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1008
1009 // Okay, this is a simple enough basic block. See if any phi values are
1010 // constants.
1011 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1012 ConstantInt *CB;
1013 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1014 CB->getType() == Type::getInt1Ty(BB->getContext())) {
1015 // Okay, we now know that all edges from PredBB should be revectored to
1016 // branch to RealDest.
1017 BasicBlock *PredBB = PN->getIncomingBlock(i);
1018 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1019
1020 if (RealDest == BB) continue; // Skip self loops.
1021
1022 // The dest block might have PHI nodes, other predecessors and other
1023 // difficult cases. Instead of being smart about this, just insert a new
1024 // block that jumps to the destination block, effectively splitting
1025 // the edge we are about to create.
1026 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1027 RealDest->getName()+".critedge",
1028 RealDest->getParent(), RealDest);
1029 BranchInst::Create(RealDest, EdgeBB);
1030 PHINode *PN;
1031 for (BasicBlock::iterator BBI = RealDest->begin();
1032 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1033 Value *V = PN->getIncomingValueForBlock(BB);
1034 PN->addIncoming(V, EdgeBB);
1035 }
1036
1037 // BB may have instructions that are being threaded over. Clone these
1038 // instructions into EdgeBB. We know that there will be no uses of the
1039 // cloned instructions outside of EdgeBB.
1040 BasicBlock::iterator InsertPt = EdgeBB->begin();
1041 std::map<Value*, Value*> TranslateMap; // Track translated values.
1042 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1043 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1044 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1045 } else {
1046 // Clone the instruction.
1047 Instruction *N = BBI->clone();
1048 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1049
1050 // Update operands due to translation.
1051 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1052 i != e; ++i) {
1053 std::map<Value*, Value*>::iterator PI =
1054 TranslateMap.find(*i);
1055 if (PI != TranslateMap.end())
1056 *i = PI->second;
1057 }
1058
1059 // Check for trivial simplification.
1060 if (Constant *C = ConstantFoldInstruction(N)) {
1061 TranslateMap[BBI] = C;
1062 delete N; // Constant folded away, don't need actual inst
1063 } else {
1064 // Insert the new instruction into its new home.
1065 EdgeBB->getInstList().insert(InsertPt, N);
1066 if (!BBI->use_empty())
1067 TranslateMap[BBI] = N;
1068 }
1069 }
1070 }
1071
1072 // Loop over all of the edges from PredBB to BB, changing them to branch
1073 // to EdgeBB instead.
1074 TerminatorInst *PredBBTI = PredBB->getTerminator();
1075 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1076 if (PredBBTI->getSuccessor(i) == BB) {
1077 BB->removePredecessor(PredBB);
1078 PredBBTI->setSuccessor(i, EdgeBB);
1079 }
1080
1081 // Recurse, simplifying any other constants.
1082 return FoldCondBranchOnPHI(BI) | true;
1083 }
1084 }
1085
1086 return false;
1087}
1088
1089/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1090/// PHI node, see if we can eliminate it.
1091static bool FoldTwoEntryPHINode(PHINode *PN) {
1092 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1093 // statement", which has a very simple dominance structure. Basically, we
1094 // are trying to find the condition that is being branched on, which
1095 // subsequently causes this merge to happen. We really want control
1096 // dependence information for this check, but simplifycfg can't keep it up
1097 // to date, and this catches most of the cases we care about anyway.
1098 //
1099 BasicBlock *BB = PN->getParent();
1100 BasicBlock *IfTrue, *IfFalse;
1101 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1102 if (!IfCond) return false;
1103
1104 // Okay, we found that we can merge this two-entry phi node into a select.
1105 // Doing so would require us to fold *all* two entry phi nodes in this block.
1106 // At some point this becomes non-profitable (particularly if the target
1107 // doesn't support cmov's). Only do this transformation if there are two or
1108 // fewer PHI nodes in this block.
1109 unsigned NumPhis = 0;
1110 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1111 if (NumPhis > 2)
1112 return false;
1113
1114 DEBUG(errs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1115 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1116
1117 // Loop over the PHI's seeing if we can promote them all to select
1118 // instructions. While we are at it, keep track of the instructions
1119 // that need to be moved to the dominating block.
1120 std::set<Instruction*> AggressiveInsts;
1121
1122 BasicBlock::iterator AfterPHIIt = BB->begin();
1123 while (isa<PHINode>(AfterPHIIt)) {
1124 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1125 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1126 if (PN->getIncomingValue(0) != PN)
1127 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1128 else
1129 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1130 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1131 &AggressiveInsts) ||
1132 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1133 &AggressiveInsts)) {
1134 return false;
1135 }
1136 }
1137
1138 // If we all PHI nodes are promotable, check to make sure that all
1139 // instructions in the predecessor blocks can be promoted as well. If
1140 // not, we won't be able to get rid of the control flow, so it's not
1141 // worth promoting to select instructions.
1142 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1143 PN = cast<PHINode>(BB->begin());
1144 BasicBlock *Pred = PN->getIncomingBlock(0);
1145 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1146 IfBlock1 = Pred;
1147 DomBlock = *pred_begin(Pred);
1148 for (BasicBlock::iterator I = Pred->begin();
1149 !isa<TerminatorInst>(I); ++I)
1150 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1151 // This is not an aggressive instruction that we can promote.
1152 // Because of this, we won't be able to get rid of the control
1153 // flow, so the xform is not worth it.
1154 return false;
1155 }
1156 }
1157
1158 Pred = PN->getIncomingBlock(1);
1159 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1160 IfBlock2 = Pred;
1161 DomBlock = *pred_begin(Pred);
1162 for (BasicBlock::iterator I = Pred->begin();
1163 !isa<TerminatorInst>(I); ++I)
1164 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1165 // This is not an aggressive instruction that we can promote.
1166 // Because of this, we won't be able to get rid of the control
1167 // flow, so the xform is not worth it.
1168 return false;
1169 }
1170 }
1171
1172 // If we can still promote the PHI nodes after this gauntlet of tests,
1173 // do all of the PHI's now.
1174
1175 // Move all 'aggressive' instructions, which are defined in the
1176 // conditional parts of the if's up to the dominating block.
1177 if (IfBlock1) {
1178 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1179 IfBlock1->getInstList(),
1180 IfBlock1->begin(),
1181 IfBlock1->getTerminator());
1182 }
1183 if (IfBlock2) {
1184 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1185 IfBlock2->getInstList(),
1186 IfBlock2->begin(),
1187 IfBlock2->getTerminator());
1188 }
1189
1190 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1191 // Change the PHI node into a select instruction.
1192 Value *TrueVal =
1193 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1194 Value *FalseVal =
1195 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1196
1197 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1198 PN->replaceAllUsesWith(NV);
1199 NV->takeName(PN);
1200
1201 BB->getInstList().erase(PN);
1202 }
1203 return true;
1204}
1205
1206/// isTerminatorFirstRelevantInsn - Return true if Term is very first
1207/// instruction ignoring Phi nodes and dbg intrinsics.
1208static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1209 BasicBlock::iterator BBI = Term;
1210 while (BBI != BB->begin()) {
1211 --BBI;
1212 if (!isa<DbgInfoIntrinsic>(BBI))
1213 break;
1214 }
1215
1216 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1217 return true;
1218 return false;
1219}
1220
1221/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1222/// to two returning blocks, try to merge them together into one return,
1223/// introducing a select if the return values disagree.
1224static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1225 assert(BI->isConditional() && "Must be a conditional branch");
1226 BasicBlock *TrueSucc = BI->getSuccessor(0);
1227 BasicBlock *FalseSucc = BI->getSuccessor(1);
1228 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1229 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1230
1231 // Check to ensure both blocks are empty (just a return) or optionally empty
1232 // with PHI nodes. If there are other instructions, merging would cause extra
1233 // computation on one path or the other.
1234 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1235 return false;
1236 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1237 return false;
1238
1239 // Okay, we found a branch that is going to two return nodes. If
1240 // there is no return value for this function, just change the
1241 // branch into a return.
1242 if (FalseRet->getNumOperands() == 0) {
1243 TrueSucc->removePredecessor(BI->getParent());
1244 FalseSucc->removePredecessor(BI->getParent());
1245 ReturnInst::Create(BI->getContext(), 0, BI);
1246 EraseTerminatorInstAndDCECond(BI);
1247 return true;
1248 }
1249
1250 // Otherwise, figure out what the true and false return values are
1251 // so we can insert a new select instruction.
1252 Value *TrueValue = TrueRet->getReturnValue();
1253 Value *FalseValue = FalseRet->getReturnValue();
1254
1255 // Unwrap any PHI nodes in the return blocks.
1256 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1257 if (TVPN->getParent() == TrueSucc)
1258 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1259 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1260 if (FVPN->getParent() == FalseSucc)
1261 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1262
1263 // In order for this transformation to be safe, we must be able to
1264 // unconditionally execute both operands to the return. This is
1265 // normally the case, but we could have a potentially-trapping
1266 // constant expression that prevents this transformation from being
1267 // safe.
1268 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1269 if (TCV->canTrap())
1270 return false;
1271 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1272 if (FCV->canTrap())
1273 return false;
1274
1275 // Okay, we collected all the mapped values and checked them for sanity, and
1276 // defined to really do this transformation. First, update the CFG.
1277 TrueSucc->removePredecessor(BI->getParent());
1278 FalseSucc->removePredecessor(BI->getParent());
1279
1280 // Insert select instructions where needed.
1281 Value *BrCond = BI->getCondition();
1282 if (TrueValue) {
1283 // Insert a select if the results differ.
1284 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1285 } else if (isa<UndefValue>(TrueValue)) {
1286 TrueValue = FalseValue;
1287 } else {
1288 TrueValue = SelectInst::Create(BrCond, TrueValue,
1289 FalseValue, "retval", BI);
1290 }
1291 }
1292
1293 Value *RI = !TrueValue ?
1294 ReturnInst::Create(BI->getContext(), BI) :
1295 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1296 (void) RI;
1297
1298 DEBUG(errs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1299 << "\n " << *BI << "NewRet = " << *RI
1300 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1301
1302 EraseTerminatorInstAndDCECond(BI);
1303
1304 return true;
1305}
1306
1307/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1308/// and if a predecessor branches to us and one of our successors, fold the
1309/// setcc into the predecessor and use logical operations to pick the right
1310/// destination.
1311bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1312 BasicBlock *BB = BI->getParent();
1313 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1314 if (Cond == 0) return false;
1315
1316
1317 // Only allow this if the condition is a simple instruction that can be
1318 // executed unconditionally. It must be in the same block as the branch, and
1319 // must be at the front of the block.
1320 BasicBlock::iterator FrontIt = BB->front();
1321 // Ignore dbg intrinsics.
1322 while(isa<DbgInfoIntrinsic>(FrontIt))
1323 ++FrontIt;
1324 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1325 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1326 return false;
1327 }
1328
1329 // Make sure the instruction after the condition is the cond branch.
1330 BasicBlock::iterator CondIt = Cond; ++CondIt;
1331 // Ingore dbg intrinsics.
1332 while(isa<DbgInfoIntrinsic>(CondIt))
1333 ++CondIt;
1334 if (&*CondIt != BI) {
1335 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1336 return false;
1337 }
1338
1339 // Cond is known to be a compare or binary operator. Check to make sure that
1340 // neither operand is a potentially-trapping constant expression.
1341 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1342 if (CE->canTrap())
1343 return false;
1344 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1345 if (CE->canTrap())
1346 return false;
1347
1348
1349 // Finally, don't infinitely unroll conditional loops.
1350 BasicBlock *TrueDest = BI->getSuccessor(0);
1351 BasicBlock *FalseDest = BI->getSuccessor(1);
1352 if (TrueDest == BB || FalseDest == BB)
1353 return false;
1354
1355 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1356 BasicBlock *PredBlock = *PI;
1357 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1358
1359 // Check that we have two conditional branches. If there is a PHI node in
1360 // the common successor, verify that the same value flows in from both
1361 // blocks.
1362 if (PBI == 0 || PBI->isUnconditional() ||
1363 !SafeToMergeTerminators(BI, PBI))
1364 continue;
1365
1366 Instruction::BinaryOps Opc;
1367 bool InvertPredCond = false;
1368
1369 if (PBI->getSuccessor(0) == TrueDest)
1370 Opc = Instruction::Or;
1371 else if (PBI->getSuccessor(1) == FalseDest)
1372 Opc = Instruction::And;
1373 else if (PBI->getSuccessor(0) == FalseDest)
1374 Opc = Instruction::And, InvertPredCond = true;
1375 else if (PBI->getSuccessor(1) == TrueDest)
1376 Opc = Instruction::Or, InvertPredCond = true;
1377 else
1378 continue;
1379
1380 DEBUG(errs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1381
1382 // If we need to invert the condition in the pred block to match, do so now.
1383 if (InvertPredCond) {
1384 Value *NewCond =
1385 BinaryOperator::CreateNot(PBI->getCondition(),
1386 PBI->getCondition()->getName()+".not", PBI);
1387 PBI->setCondition(NewCond);
1388 BasicBlock *OldTrue = PBI->getSuccessor(0);
1389 BasicBlock *OldFalse = PBI->getSuccessor(1);
1390 PBI->setSuccessor(0, OldFalse);
1391 PBI->setSuccessor(1, OldTrue);
1392 }
1393
1394 // Clone Cond into the predecessor basic block, and or/and the
1395 // two conditions together.
1396 Instruction *New = Cond->clone();
1397 PredBlock->getInstList().insert(PBI, New);
1398 New->takeName(Cond);
1399 Cond->setName(New->getName()+".old");
1400
1401 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1402 New, "or.cond", PBI);
1403 PBI->setCondition(NewCond);
1404 if (PBI->getSuccessor(0) == BB) {
1405 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1406 PBI->setSuccessor(0, TrueDest);
1407 }
1408 if (PBI->getSuccessor(1) == BB) {
1409 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1410 PBI->setSuccessor(1, FalseDest);
1411 }
1412 return true;
1413 }
1414 return false;
1415}
1416
1417/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1418/// predecessor of another block, this function tries to simplify it. We know
1419/// that PBI and BI are both conditional branches, and BI is in one of the
1420/// successor blocks of PBI - PBI branches to BI.
1421static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1422 assert(PBI->isConditional() && BI->isConditional());
1423 BasicBlock *BB = BI->getParent();
1424
1425 // If this block ends with a branch instruction, and if there is a
1426 // predecessor that ends on a branch of the same condition, make
1427 // this conditional branch redundant.
1428 if (PBI->getCondition() == BI->getCondition() &&
1429 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1430 // Okay, the outcome of this conditional branch is statically
1431 // knowable. If this block had a single pred, handle specially.
1432 if (BB->getSinglePredecessor()) {
1433 // Turn this into a branch on constant.
1434 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1435 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1436 CondIsTrue));
1437 return true; // Nuke the branch on constant.
1438 }
1439
1440 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1441 // in the constant and simplify the block result. Subsequent passes of
1442 // simplifycfg will thread the block.
1443 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1444 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1445 BI->getCondition()->getName() + ".pr",
1446 BB->begin());
1447 // Okay, we're going to insert the PHI node. Since PBI is not the only
1448 // predecessor, compute the PHI'd conditional value for all of the preds.
1449 // Any predecessor where the condition is not computable we keep symbolic.
1450 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1451 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1452 PBI != BI && PBI->isConditional() &&
1453 PBI->getCondition() == BI->getCondition() &&
1454 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1455 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1456 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1457 CondIsTrue), *PI);
1458 } else {
1459 NewPN->addIncoming(BI->getCondition(), *PI);
1460 }
1461
1462 BI->setCondition(NewPN);
1463 return true;
1464 }
1465 }
1466
1467 // If this is a conditional branch in an empty block, and if any
1468 // predecessors is a conditional branch to one of our destinations,
1469 // fold the conditions into logical ops and one cond br.
1470 BasicBlock::iterator BBI = BB->begin();
1471 // Ignore dbg intrinsics.
1472 while (isa<DbgInfoIntrinsic>(BBI))
1473 ++BBI;
1474 if (&*BBI != BI)
1475 return false;
1476
1477
1478 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1479 if (CE->canTrap())
1480 return false;
1481
1482 int PBIOp, BIOp;
1483 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1484 PBIOp = BIOp = 0;
1485 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1486 PBIOp = 0, BIOp = 1;
1487 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1488 PBIOp = 1, BIOp = 0;
1489 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1490 PBIOp = BIOp = 1;
1491 else
1492 return false;
1493
1494 // Check to make sure that the other destination of this branch
1495 // isn't BB itself. If so, this is an infinite loop that will
1496 // keep getting unwound.
1497 if (PBI->getSuccessor(PBIOp) == BB)
1498 return false;
1499
1500 // Do not perform this transformation if it would require
1501 // insertion of a large number of select instructions. For targets
1502 // without predication/cmovs, this is a big pessimization.
1503 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1504
1505 unsigned NumPhis = 0;
1506 for (BasicBlock::iterator II = CommonDest->begin();
1507 isa<PHINode>(II); ++II, ++NumPhis)
1508 if (NumPhis > 2) // Disable this xform.
1509 return false;
1510
1511 // Finally, if everything is ok, fold the branches to logical ops.
1512 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1513
1514 DEBUG(errs() << "FOLDING BRs:" << *PBI->getParent()
1515 << "AND: " << *BI->getParent());
1516
1517
1518 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1519 // branch in it, where one edge (OtherDest) goes back to itself but the other
1520 // exits. We don't *know* that the program avoids the infinite loop
1521 // (even though that seems likely). If we do this xform naively, we'll end up
1522 // recursively unpeeling the loop. Since we know that (after the xform is
1523 // done) that the block *is* infinite if reached, we just make it an obviously
1524 // infinite loop with no cond branch.
1525 if (OtherDest == BB) {
1526 // Insert it at the end of the function, because it's either code,
1527 // or it won't matter if it's hot. :)
1528 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1529 "infloop", BB->getParent());
1530 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1531 OtherDest = InfLoopBlock;
1532 }
1533
1534 DEBUG(errs() << *PBI->getParent()->getParent());
1535
1536 // BI may have other predecessors. Because of this, we leave
1537 // it alone, but modify PBI.
1538
1539 // Make sure we get to CommonDest on True&True directions.
1540 Value *PBICond = PBI->getCondition();
1541 if (PBIOp)
1542 PBICond = BinaryOperator::CreateNot(PBICond,
1543 PBICond->getName()+".not",
1544 PBI);
1545 Value *BICond = BI->getCondition();
1546 if (BIOp)
1547 BICond = BinaryOperator::CreateNot(BICond,
1548 BICond->getName()+".not",
1549 PBI);
1550 // Merge the conditions.
1551 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1552
1553 // Modify PBI to branch on the new condition to the new dests.
1554 PBI->setCondition(Cond);
1555 PBI->setSuccessor(0, CommonDest);
1556 PBI->setSuccessor(1, OtherDest);
1557
1558 // OtherDest may have phi nodes. If so, add an entry from PBI's
1559 // block that are identical to the entries for BI's block.
1560 PHINode *PN;
1561 for (BasicBlock::iterator II = OtherDest->begin();
1562 (PN = dyn_cast<PHINode>(II)); ++II) {
1563 Value *V = PN->getIncomingValueForBlock(BB);
1564 PN->addIncoming(V, PBI->getParent());
1565 }
1566
1567 // We know that the CommonDest already had an edge from PBI to
1568 // it. If it has PHIs though, the PHIs may have different
1569 // entries for BB and PBI's BB. If so, insert a select to make
1570 // them agree.
1571 for (BasicBlock::iterator II = CommonDest->begin();
1572 (PN = dyn_cast<PHINode>(II)); ++II) {
1573 Value *BIV = PN->getIncomingValueForBlock(BB);
1574 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1575 Value *PBIV = PN->getIncomingValue(PBBIdx);
1576 if (BIV != PBIV) {
1577 // Insert a select in PBI to pick the right value.
1578 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1579 PBIV->getName()+".mux", PBI);
1580 PN->setIncomingValue(PBBIdx, NV);
1581 }
1582 }
1583
1584 DEBUG(errs() << "INTO: " << *PBI->getParent());
1585 DEBUG(errs() << *PBI->getParent()->getParent());
1586
1587 // This basic block is probably dead. We know it has at least
1588 // one fewer predecessor.
1589 return true;
1590}
1591
1592/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
1593/// nodes in this block. This doesn't try to be clever about PHI nodes
1594/// which differ only in the order of the incoming values, but instcombine
1595/// orders them so it usually won't matter.
1596///
|
1598 bool Changed = false;
1599
1600 // This implementation doesn't currently consider undef operands
1601 // specially. Theroetically, two phis which are identical except for
1602 // one having an undef where the other doesn't could be collapsed.
1603
1604 // Map from PHI hash values to PHI nodes. If multiple PHIs have
1605 // the same hash value, the element is the first PHI in the
1606 // linked list in CollisionMap.
1607 DenseMap<uintptr_t, PHINode *> HashMap;
1608
1609 // Maintain linked lists of PHI nodes with common hash values.
1610 DenseMap<PHINode *, PHINode *> CollisionMap;
1611
1612 // Examine each PHI.
1613 for (BasicBlock::iterator I = BB->begin();
1614 PHINode *PN = dyn_cast<PHINode>(I++); ) {
1615 // Compute a hash value on the operands. Instcombine will likely have sorted
1616 // them, which helps expose duplicates, but we have to check all the
1617 // operands to be safe in case instcombine hasn't run.
1618 uintptr_t Hash = 0;
1619 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
1620 // This hash algorithm is quite weak as hash functions go, but it seems
1621 // to do a good enough job for this particular purpose, and is very quick.
1622 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
1623 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
1624 }
1625 // If we've never seen this hash value before, it's a unique PHI.
1626 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
1627 HashMap.insert(std::make_pair(Hash, PN));
1628 if (Pair.second) continue;
1629 // Otherwise it's either a duplicate or a hash collision.
1630 for (PHINode *OtherPN = Pair.first->second; ; ) {
1631 if (OtherPN->isIdenticalTo(PN)) {
1632 // A duplicate. Replace this PHI with its duplicate.
1633 PN->replaceAllUsesWith(OtherPN);
1634 PN->eraseFromParent();
1635 Changed = true;
1636 break;
1637 }
1638 // A non-duplicate hash collision.
1639 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
1640 if (I == CollisionMap.end()) {
1641 // Set this PHI to be the head of the linked list of colliding PHIs.
1642 PHINode *Old = Pair.first->second;
1643 Pair.first->second = PN;
1644 CollisionMap[PN] = Old;
1645 break;
1646 }
1647 // Procede to the next PHI in the list.
1648 OtherPN = I->second;
1649 }
1650 }
1651
1652 return Changed;
1653}
1654
1655/// SimplifyCFG - This function is used to do simplification of a CFG. For
1656/// example, it adjusts branches to branches to eliminate the extra hop, it
1657/// eliminates unreachable basic blocks, and does other "peephole" optimization
1658/// of the CFG. It returns true if a modification was made.
1659///
1660/// WARNING: The entry node of a function may not be simplified.
1661///
1662bool llvm::SimplifyCFG(BasicBlock *BB) {
1663 bool Changed = false;
1664 Function *M = BB->getParent();
1665
1666 assert(BB && BB->getParent() && "Block not embedded in function!");
1667 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1668 assert(&BB->getParent()->getEntryBlock() != BB &&
1669 "Can't Simplify entry block!");
1670
1671 // Remove basic blocks that have no predecessors... or that just have themself
1672 // as a predecessor. These are unreachable.
1673 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1674 DEBUG(errs() << "Removing BB: \n" << *BB);
1675 DeleteDeadBlock(BB);
1676 return true;
1677 }
1678
1679 // Check to see if we can constant propagate this terminator instruction
1680 // away...
1681 Changed |= ConstantFoldTerminator(BB);
1682
1683 // Check for and eliminate duplicate PHI nodes in this block.
1684 Changed |= EliminateDuplicatePHINodes(BB);
1685
1686 // If there is a trivial two-entry PHI node in this basic block, and we can
1687 // eliminate it, do so now.
1688 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1689 if (PN->getNumIncomingValues() == 2)
1690 Changed |= FoldTwoEntryPHINode(PN);
1691
1692 // If this is a returning block with only PHI nodes in it, fold the return
1693 // instruction into any unconditional branch predecessors.
1694 //
1695 // If any predecessor is a conditional branch that just selects among
1696 // different return values, fold the replace the branch/return with a select
1697 // and return.
1698 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1699 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1700 // Find predecessors that end with branches.
1701 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1702 SmallVector<BranchInst*, 8> CondBranchPreds;
1703 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1704 TerminatorInst *PTI = (*PI)->getTerminator();
1705 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1706 if (BI->isUnconditional())
1707 UncondBranchPreds.push_back(*PI);
1708 else
1709 CondBranchPreds.push_back(BI);
1710 }
1711 }
1712
1713 // If we found some, do the transformation!
1714 if (!UncondBranchPreds.empty()) {
1715 while (!UncondBranchPreds.empty()) {
1716 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1717 DEBUG(errs() << "FOLDING: " << *BB
1718 << "INTO UNCOND BRANCH PRED: " << *Pred);
1719 Instruction *UncondBranch = Pred->getTerminator();
1720 // Clone the return and add it to the end of the predecessor.
1721 Instruction *NewRet = RI->clone();
1722 Pred->getInstList().push_back(NewRet);
1723
1724 BasicBlock::iterator BBI = RI;
1725 if (BBI != BB->begin()) {
1726 // Move region end info into the predecessor.
1727 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1728 DREI->moveBefore(NewRet);
1729 }
1730
1731 // If the return instruction returns a value, and if the value was a
1732 // PHI node in "BB", propagate the right value into the return.
1733 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1734 i != e; ++i)
1735 if (PHINode *PN = dyn_cast<PHINode>(*i))
1736 if (PN->getParent() == BB)
1737 *i = PN->getIncomingValueForBlock(Pred);
1738
1739 // Update any PHI nodes in the returning block to realize that we no
1740 // longer branch to them.
1741 BB->removePredecessor(Pred);
1742 Pred->getInstList().erase(UncondBranch);
1743 }
1744
1745 // If we eliminated all predecessors of the block, delete the block now.
1746 if (pred_begin(BB) == pred_end(BB))
1747 // We know there are no successors, so just nuke the block.
1748 M->getBasicBlockList().erase(BB);
1749
1750 return true;
1751 }
1752
1753 // Check out all of the conditional branches going to this return
1754 // instruction. If any of them just select between returns, change the
1755 // branch itself into a select/return pair.
1756 while (!CondBranchPreds.empty()) {
1757 BranchInst *BI = CondBranchPreds.pop_back_val();
1758
1759 // Check to see if the non-BB successor is also a return block.
1760 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1761 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1762 SimplifyCondBranchToTwoReturns(BI))
1763 return true;
1764 }
1765 }
1766 } else if (isa<UnwindInst>(BB->begin())) {
1767 // Check to see if the first instruction in this block is just an unwind.
1768 // If so, replace any invoke instructions which use this as an exception
1769 // destination with call instructions.
1770 //
1771 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1772 while (!Preds.empty()) {
1773 BasicBlock *Pred = Preds.back();
1774 if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1775 if (II->getUnwindDest() == BB) {
1776 // Insert a new branch instruction before the invoke, because this
1777 // is now a fall through.
1778 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1779 Pred->getInstList().remove(II); // Take out of symbol table
1780
1781 // Insert the call now.
1782 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1783 CallInst *CI = CallInst::Create(II->getCalledValue(),
1784 Args.begin(), Args.end(),
1785 II->getName(), BI);
1786 CI->setCallingConv(II->getCallingConv());
1787 CI->setAttributes(II->getAttributes());
1788 // If the invoke produced a value, the Call now does instead.
1789 II->replaceAllUsesWith(CI);
1790 delete II;
1791 Changed = true;
1792 }
1793
1794 Preds.pop_back();
1795 }
1796
1797 // If this block is now dead, remove it.
1798 if (pred_begin(BB) == pred_end(BB)) {
1799 // We know there are no successors, so just nuke the block.
1800 M->getBasicBlockList().erase(BB);
1801 return true;
1802 }
1803
1804 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1805 if (isValueEqualityComparison(SI)) {
1806 // If we only have one predecessor, and if it is a branch on this value,
1807 // see if that predecessor totally determines the outcome of this switch.
1808 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1809 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1810 return SimplifyCFG(BB) || 1;
1811
1812 // If the block only contains the switch, see if we can fold the block
1813 // away into any preds.
1814 BasicBlock::iterator BBI = BB->begin();
1815 // Ignore dbg intrinsics.
1816 while (isa<DbgInfoIntrinsic>(BBI))
1817 ++BBI;
1818 if (SI == &*BBI)
1819 if (FoldValueComparisonIntoPredecessors(SI))
1820 return SimplifyCFG(BB) || 1;
1821 }
1822 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1823 if (BI->isUnconditional()) {
1824 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1825
1826 // Ignore dbg intrinsics.
1827 while (isa<DbgInfoIntrinsic>(BBI))
1828 ++BBI;
1829 if (BBI->isTerminator()) // Terminator is the only non-phi instruction!
1830 if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
1831 return true;
1832
1833 } else { // Conditional branch
1834 if (isValueEqualityComparison(BI)) {
1835 // If we only have one predecessor, and if it is a branch on this value,
1836 // see if that predecessor totally determines the outcome of this
1837 // switch.
1838 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1839 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1840 return SimplifyCFG(BB) || 1;
1841
1842 // This block must be empty, except for the setcond inst, if it exists.
1843 // Ignore dbg intrinsics.
1844 BasicBlock::iterator I = BB->begin();
1845 // Ignore dbg intrinsics.
1846 while (isa<DbgInfoIntrinsic>(I))
1847 ++I;
1848 if (&*I == BI) {
1849 if (FoldValueComparisonIntoPredecessors(BI))
1850 return SimplifyCFG(BB) | true;
1851 } else if (&*I == cast<Instruction>(BI->getCondition())){
1852 ++I;
1853 // Ignore dbg intrinsics.
1854 while (isa<DbgInfoIntrinsic>(I))
1855 ++I;
1856 if(&*I == BI) {
1857 if (FoldValueComparisonIntoPredecessors(BI))
1858 return SimplifyCFG(BB) | true;
1859 }
1860 }
1861 }
1862
1863 // If this is a branch on a phi node in the current block, thread control
1864 // through this block if any PHI node entries are constants.
1865 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1866 if (PN->getParent() == BI->getParent())
1867 if (FoldCondBranchOnPHI(BI))
1868 return SimplifyCFG(BB) | true;
1869
1870 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1871 // branches to us and one of our successors, fold the setcc into the
1872 // predecessor and use logical operations to pick the right destination.
1873 if (FoldBranchToCommonDest(BI))
1874 return SimplifyCFG(BB) | 1;
1875
1876
1877 // Scan predecessor blocks for conditional branches.
1878 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1879 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1880 if (PBI != BI && PBI->isConditional())
1881 if (SimplifyCondBranchToCondBranch(PBI, BI))
1882 return SimplifyCFG(BB) | true;
1883 }
1884 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1885 // If there are any instructions immediately before the unreachable that can
1886 // be removed, do so.
1887 Instruction *Unreachable = BB->getTerminator();
1888 while (Unreachable != BB->begin()) {
1889 BasicBlock::iterator BBI = Unreachable;
1890 --BBI;
1891 // Do not delete instructions that can have side effects, like calls
1892 // (which may never return) and volatile loads and stores.
1893 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
1894
1895 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1896 if (SI->isVolatile())
1897 break;
1898
1899 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1900 if (LI->isVolatile())
1901 break;
1902
1903 // Delete this instruction
1904 BB->getInstList().erase(BBI);
1905 Changed = true;
1906 }
1907
1908 // If the unreachable instruction is the first in the block, take a gander
1909 // at all of the predecessors of this instruction, and simplify them.
1910 if (&BB->front() == Unreachable) {
1911 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1912 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1913 TerminatorInst *TI = Preds[i]->getTerminator();
1914
1915 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1916 if (BI->isUnconditional()) {
1917 if (BI->getSuccessor(0) == BB) {
1918 new UnreachableInst(TI->getContext(), TI);
1919 TI->eraseFromParent();
1920 Changed = true;
1921 }
1922 } else {
1923 if (BI->getSuccessor(0) == BB) {
1924 BranchInst::Create(BI->getSuccessor(1), BI);
1925 EraseTerminatorInstAndDCECond(BI);
1926 } else if (BI->getSuccessor(1) == BB) {
1927 BranchInst::Create(BI->getSuccessor(0), BI);
1928 EraseTerminatorInstAndDCECond(BI);
1929 Changed = true;
1930 }
1931 }
1932 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1933 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1934 if (SI->getSuccessor(i) == BB) {
1935 BB->removePredecessor(SI->getParent());
1936 SI->removeCase(i);
1937 --i; --e;
1938 Changed = true;
1939 }
1940 // If the default value is unreachable, figure out the most popular
1941 // destination and make it the default.
1942 if (SI->getSuccessor(0) == BB) {
1943 std::map<BasicBlock*, unsigned> Popularity;
1944 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1945 Popularity[SI->getSuccessor(i)]++;
1946
1947 // Find the most popular block.
1948 unsigned MaxPop = 0;
1949 BasicBlock *MaxBlock = 0;
1950 for (std::map<BasicBlock*, unsigned>::iterator
1951 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1952 if (I->second > MaxPop) {
1953 MaxPop = I->second;
1954 MaxBlock = I->first;
1955 }
1956 }
1957 if (MaxBlock) {
1958 // Make this the new default, allowing us to delete any explicit
1959 // edges to it.
1960 SI->setSuccessor(0, MaxBlock);
1961 Changed = true;
1962
1963 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1964 // it.
1965 if (isa<PHINode>(MaxBlock->begin()))
1966 for (unsigned i = 0; i != MaxPop-1; ++i)
1967 MaxBlock->removePredecessor(SI->getParent());
1968
1969 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1970 if (SI->getSuccessor(i) == MaxBlock) {
1971 SI->removeCase(i);
1972 --i; --e;
1973 }
1974 }
1975 }
1976 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1977 if (II->getUnwindDest() == BB) {
1978 // Convert the invoke to a call instruction. This would be a good
1979 // place to note that the call does not throw though.
1980 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1981 II->removeFromParent(); // Take out of symbol table
1982
1983 // Insert the call now...
1984 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
1985 CallInst *CI = CallInst::Create(II->getCalledValue(),
1986 Args.begin(), Args.end(),
1987 II->getName(), BI);
1988 CI->setCallingConv(II->getCallingConv());
1989 CI->setAttributes(II->getAttributes());
1990 // If the invoke produced a value, the Call does now instead.
1991 II->replaceAllUsesWith(CI);
1992 delete II;
1993 Changed = true;
1994 }
1995 }
1996 }
1997
1998 // If this block is now dead, remove it.
1999 if (pred_begin(BB) == pred_end(BB)) {
2000 // We know there are no successors, so just nuke the block.
2001 M->getBasicBlockList().erase(BB);
2002 return true;
2003 }
2004 }
2005 }
2006
2007 // Merge basic blocks into their predecessor if there is only one distinct
2008 // pred, and if there is only one distinct successor of the predecessor, and
2009 // if there are no PHI nodes.
2010 //
2011 if (MergeBlockIntoPredecessor(BB))
2012 return true;
2013
2014 // Otherwise, if this block only has a single predecessor, and if that block
2015 // is a conditional branch, see if we can hoist any code from this block up
2016 // into our predecessor.
2017 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2018 BasicBlock *OnlyPred = *PI++;
2019 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2020 if (*PI != OnlyPred) {
2021 OnlyPred = 0; // There are multiple different predecessors...
2022 break;
2023 }
2024
2025 if (OnlyPred)
2026 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2027 if (BI->isConditional()) {
2028 // Get the other block.
2029 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2030 PI = pred_begin(OtherBB);
2031 ++PI;
2032
2033 if (PI == pred_end(OtherBB)) {
2034 // We have a conditional branch to two blocks that are only reachable
2035 // from the condbr. We know that the condbr dominates the two blocks,
2036 // so see if there is any identical code in the "then" and "else"
2037 // blocks. If so, we can hoist it up to the branching block.
2038 Changed |= HoistThenElseCodeToIf(BI);
2039 } else {
2040 BasicBlock* OnlySucc = NULL;
2041 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2042 SI != SE; ++SI) {
2043 if (!OnlySucc)
2044 OnlySucc = *SI;
2045 else if (*SI != OnlySucc) {
2046 OnlySucc = 0; // There are multiple distinct successors!
2047 break;
2048 }
2049 }
2050
2051 if (OnlySucc == OtherBB) {
2052 // If BB's only successor is the other successor of the predecessor,
2053 // i.e. a triangle, see if we can hoist any code from this block up
2054 // to the "if" block.
2055 Changed |= SpeculativelyExecuteBB(BI, BB);
2056 }
2057 }
2058 }
2059
2060 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2061 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2062 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2063 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2064 Instruction *Cond = cast<Instruction>(BI->getCondition());
2065 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2066 // 'setne's and'ed together, collect them.
2067 Value *CompVal = 0;
2068 std::vector<ConstantInt*> Values;
2069 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2070 if (CompVal && CompVal->getType()->isInteger()) {
2071 // There might be duplicate constants in the list, which the switch
2072 // instruction can't handle, remove them now.
2073 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2074 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2075
2076 // Figure out which block is which destination.
2077 BasicBlock *DefaultBB = BI->getSuccessor(1);
2078 BasicBlock *EdgeBB = BI->getSuccessor(0);
2079 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2080
2081 // Create the new switch instruction now.
2082 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2083 Values.size(), BI);
2084
2085 // Add all of the 'cases' to the switch instruction.
2086 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2087 New->addCase(Values[i], EdgeBB);
2088
2089 // We added edges from PI to the EdgeBB. As such, if there were any
2090 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2091 // the number of edges added.
2092 for (BasicBlock::iterator BBI = EdgeBB->begin();
2093 isa<PHINode>(BBI); ++BBI) {
2094 PHINode *PN = cast<PHINode>(BBI);
2095 Value *InVal = PN->getIncomingValueForBlock(*PI);
2096 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2097 PN->addIncoming(InVal, *PI);
2098 }
2099
2100 // Erase the old branch instruction.
2101 EraseTerminatorInstAndDCECond(BI);
2102 return true;
2103 }
2104 }
2105
2106 return Changed;
2107}
| 1598 bool Changed = false;
1599
1600 // This implementation doesn't currently consider undef operands
1601 // specially. Theroetically, two phis which are identical except for
1602 // one having an undef where the other doesn't could be collapsed.
1603
1604 // Map from PHI hash values to PHI nodes. If multiple PHIs have
1605 // the same hash value, the element is the first PHI in the
1606 // linked list in CollisionMap.
1607 DenseMap<uintptr_t, PHINode *> HashMap;
1608
1609 // Maintain linked lists of PHI nodes with common hash values.
1610 DenseMap<PHINode *, PHINode *> CollisionMap;
1611
1612 // Examine each PHI.
1613 for (BasicBlock::iterator I = BB->begin();
1614 PHINode *PN = dyn_cast<PHINode>(I++); ) {
1615 // Compute a hash value on the operands. Instcombine will likely have sorted
1616 // them, which helps expose duplicates, but we have to check all the
1617 // operands to be safe in case instcombine hasn't run.
1618 uintptr_t Hash = 0;
1619 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
1620 // This hash algorithm is quite weak as hash functions go, but it seems
1621 // to do a good enough job for this particular purpose, and is very quick.
1622 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
1623 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
1624 }
1625 // If we've never seen this hash value before, it's a unique PHI.
1626 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
1627 HashMap.insert(std::make_pair(Hash, PN));
1628 if (Pair.second) continue;
1629 // Otherwise it's either a duplicate or a hash collision.
1630 for (PHINode *OtherPN = Pair.first->second; ; ) {
1631 if (OtherPN->isIdenticalTo(PN)) {
1632 // A duplicate. Replace this PHI with its duplicate.
1633 PN->replaceAllUsesWith(OtherPN);
1634 PN->eraseFromParent();
1635 Changed = true;
1636 break;
1637 }
1638 // A non-duplicate hash collision.
1639 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
1640 if (I == CollisionMap.end()) {
1641 // Set this PHI to be the head of the linked list of colliding PHIs.
1642 PHINode *Old = Pair.first->second;
1643 Pair.first->second = PN;
1644 CollisionMap[PN] = Old;
1645 break;
1646 }
1647 // Procede to the next PHI in the list.
1648 OtherPN = I->second;
1649 }
1650 }
1651
1652 return Changed;
1653}
1654
1655/// SimplifyCFG - This function is used to do simplification of a CFG. For
1656/// example, it adjusts branches to branches to eliminate the extra hop, it
1657/// eliminates unreachable basic blocks, and does other "peephole" optimization
1658/// of the CFG. It returns true if a modification was made.
1659///
1660/// WARNING: The entry node of a function may not be simplified.
1661///
1662bool llvm::SimplifyCFG(BasicBlock *BB) {
1663 bool Changed = false;
1664 Function *M = BB->getParent();
1665
1666 assert(BB && BB->getParent() && "Block not embedded in function!");
1667 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1668 assert(&BB->getParent()->getEntryBlock() != BB &&
1669 "Can't Simplify entry block!");
1670
1671 // Remove basic blocks that have no predecessors... or that just have themself
1672 // as a predecessor. These are unreachable.
1673 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1674 DEBUG(errs() << "Removing BB: \n" << *BB);
1675 DeleteDeadBlock(BB);
1676 return true;
1677 }
1678
1679 // Check to see if we can constant propagate this terminator instruction
1680 // away...
1681 Changed |= ConstantFoldTerminator(BB);
1682
1683 // Check for and eliminate duplicate PHI nodes in this block.
1684 Changed |= EliminateDuplicatePHINodes(BB);
1685
1686 // If there is a trivial two-entry PHI node in this basic block, and we can
1687 // eliminate it, do so now.
1688 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1689 if (PN->getNumIncomingValues() == 2)
1690 Changed |= FoldTwoEntryPHINode(PN);
1691
1692 // If this is a returning block with only PHI nodes in it, fold the return
1693 // instruction into any unconditional branch predecessors.
1694 //
1695 // If any predecessor is a conditional branch that just selects among
1696 // different return values, fold the replace the branch/return with a select
1697 // and return.
1698 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1699 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1700 // Find predecessors that end with branches.
1701 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1702 SmallVector<BranchInst*, 8> CondBranchPreds;
1703 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1704 TerminatorInst *PTI = (*PI)->getTerminator();
1705 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1706 if (BI->isUnconditional())
1707 UncondBranchPreds.push_back(*PI);
1708 else
1709 CondBranchPreds.push_back(BI);
1710 }
1711 }
1712
1713 // If we found some, do the transformation!
1714 if (!UncondBranchPreds.empty()) {
1715 while (!UncondBranchPreds.empty()) {
1716 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1717 DEBUG(errs() << "FOLDING: " << *BB
1718 << "INTO UNCOND BRANCH PRED: " << *Pred);
1719 Instruction *UncondBranch = Pred->getTerminator();
1720 // Clone the return and add it to the end of the predecessor.
1721 Instruction *NewRet = RI->clone();
1722 Pred->getInstList().push_back(NewRet);
1723
1724 BasicBlock::iterator BBI = RI;
1725 if (BBI != BB->begin()) {
1726 // Move region end info into the predecessor.
1727 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1728 DREI->moveBefore(NewRet);
1729 }
1730
1731 // If the return instruction returns a value, and if the value was a
1732 // PHI node in "BB", propagate the right value into the return.
1733 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1734 i != e; ++i)
1735 if (PHINode *PN = dyn_cast<PHINode>(*i))
1736 if (PN->getParent() == BB)
1737 *i = PN->getIncomingValueForBlock(Pred);
1738
1739 // Update any PHI nodes in the returning block to realize that we no
1740 // longer branch to them.
1741 BB->removePredecessor(Pred);
1742 Pred->getInstList().erase(UncondBranch);
1743 }
1744
1745 // If we eliminated all predecessors of the block, delete the block now.
1746 if (pred_begin(BB) == pred_end(BB))
1747 // We know there are no successors, so just nuke the block.
1748 M->getBasicBlockList().erase(BB);
1749
1750 return true;
1751 }
1752
1753 // Check out all of the conditional branches going to this return
1754 // instruction. If any of them just select between returns, change the
1755 // branch itself into a select/return pair.
1756 while (!CondBranchPreds.empty()) {
1757 BranchInst *BI = CondBranchPreds.pop_back_val();
1758
1759 // Check to see if the non-BB successor is also a return block.
1760 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1761 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1762 SimplifyCondBranchToTwoReturns(BI))
1763 return true;
1764 }
1765 }
1766 } else if (isa<UnwindInst>(BB->begin())) {
1767 // Check to see if the first instruction in this block is just an unwind.
1768 // If so, replace any invoke instructions which use this as an exception
1769 // destination with call instructions.
1770 //
1771 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1772 while (!Preds.empty()) {
1773 BasicBlock *Pred = Preds.back();
1774 if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1775 if (II->getUnwindDest() == BB) {
1776 // Insert a new branch instruction before the invoke, because this
1777 // is now a fall through.
1778 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1779 Pred->getInstList().remove(II); // Take out of symbol table
1780
1781 // Insert the call now.
1782 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1783 CallInst *CI = CallInst::Create(II->getCalledValue(),
1784 Args.begin(), Args.end(),
1785 II->getName(), BI);
1786 CI->setCallingConv(II->getCallingConv());
1787 CI->setAttributes(II->getAttributes());
1788 // If the invoke produced a value, the Call now does instead.
1789 II->replaceAllUsesWith(CI);
1790 delete II;
1791 Changed = true;
1792 }
1793
1794 Preds.pop_back();
1795 }
1796
1797 // If this block is now dead, remove it.
1798 if (pred_begin(BB) == pred_end(BB)) {
1799 // We know there are no successors, so just nuke the block.
1800 M->getBasicBlockList().erase(BB);
1801 return true;
1802 }
1803
1804 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1805 if (isValueEqualityComparison(SI)) {
1806 // If we only have one predecessor, and if it is a branch on this value,
1807 // see if that predecessor totally determines the outcome of this switch.
1808 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1809 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1810 return SimplifyCFG(BB) || 1;
1811
1812 // If the block only contains the switch, see if we can fold the block
1813 // away into any preds.
1814 BasicBlock::iterator BBI = BB->begin();
1815 // Ignore dbg intrinsics.
1816 while (isa<DbgInfoIntrinsic>(BBI))
1817 ++BBI;
1818 if (SI == &*BBI)
1819 if (FoldValueComparisonIntoPredecessors(SI))
1820 return SimplifyCFG(BB) || 1;
1821 }
1822 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1823 if (BI->isUnconditional()) {
1824 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1825
1826 // Ignore dbg intrinsics.
1827 while (isa<DbgInfoIntrinsic>(BBI))
1828 ++BBI;
1829 if (BBI->isTerminator()) // Terminator is the only non-phi instruction!
1830 if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
1831 return true;
1832
1833 } else { // Conditional branch
1834 if (isValueEqualityComparison(BI)) {
1835 // If we only have one predecessor, and if it is a branch on this value,
1836 // see if that predecessor totally determines the outcome of this
1837 // switch.
1838 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1839 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1840 return SimplifyCFG(BB) || 1;
1841
1842 // This block must be empty, except for the setcond inst, if it exists.
1843 // Ignore dbg intrinsics.
1844 BasicBlock::iterator I = BB->begin();
1845 // Ignore dbg intrinsics.
1846 while (isa<DbgInfoIntrinsic>(I))
1847 ++I;
1848 if (&*I == BI) {
1849 if (FoldValueComparisonIntoPredecessors(BI))
1850 return SimplifyCFG(BB) | true;
1851 } else if (&*I == cast<Instruction>(BI->getCondition())){
1852 ++I;
1853 // Ignore dbg intrinsics.
1854 while (isa<DbgInfoIntrinsic>(I))
1855 ++I;
1856 if(&*I == BI) {
1857 if (FoldValueComparisonIntoPredecessors(BI))
1858 return SimplifyCFG(BB) | true;
1859 }
1860 }
1861 }
1862
1863 // If this is a branch on a phi node in the current block, thread control
1864 // through this block if any PHI node entries are constants.
1865 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1866 if (PN->getParent() == BI->getParent())
1867 if (FoldCondBranchOnPHI(BI))
1868 return SimplifyCFG(BB) | true;
1869
1870 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1871 // branches to us and one of our successors, fold the setcc into the
1872 // predecessor and use logical operations to pick the right destination.
1873 if (FoldBranchToCommonDest(BI))
1874 return SimplifyCFG(BB) | 1;
1875
1876
1877 // Scan predecessor blocks for conditional branches.
1878 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1879 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1880 if (PBI != BI && PBI->isConditional())
1881 if (SimplifyCondBranchToCondBranch(PBI, BI))
1882 return SimplifyCFG(BB) | true;
1883 }
1884 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1885 // If there are any instructions immediately before the unreachable that can
1886 // be removed, do so.
1887 Instruction *Unreachable = BB->getTerminator();
1888 while (Unreachable != BB->begin()) {
1889 BasicBlock::iterator BBI = Unreachable;
1890 --BBI;
1891 // Do not delete instructions that can have side effects, like calls
1892 // (which may never return) and volatile loads and stores.
1893 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
1894
1895 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1896 if (SI->isVolatile())
1897 break;
1898
1899 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1900 if (LI->isVolatile())
1901 break;
1902
1903 // Delete this instruction
1904 BB->getInstList().erase(BBI);
1905 Changed = true;
1906 }
1907
1908 // If the unreachable instruction is the first in the block, take a gander
1909 // at all of the predecessors of this instruction, and simplify them.
1910 if (&BB->front() == Unreachable) {
1911 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1912 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1913 TerminatorInst *TI = Preds[i]->getTerminator();
1914
1915 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1916 if (BI->isUnconditional()) {
1917 if (BI->getSuccessor(0) == BB) {
1918 new UnreachableInst(TI->getContext(), TI);
1919 TI->eraseFromParent();
1920 Changed = true;
1921 }
1922 } else {
1923 if (BI->getSuccessor(0) == BB) {
1924 BranchInst::Create(BI->getSuccessor(1), BI);
1925 EraseTerminatorInstAndDCECond(BI);
1926 } else if (BI->getSuccessor(1) == BB) {
1927 BranchInst::Create(BI->getSuccessor(0), BI);
1928 EraseTerminatorInstAndDCECond(BI);
1929 Changed = true;
1930 }
1931 }
1932 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1933 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1934 if (SI->getSuccessor(i) == BB) {
1935 BB->removePredecessor(SI->getParent());
1936 SI->removeCase(i);
1937 --i; --e;
1938 Changed = true;
1939 }
1940 // If the default value is unreachable, figure out the most popular
1941 // destination and make it the default.
1942 if (SI->getSuccessor(0) == BB) {
1943 std::map<BasicBlock*, unsigned> Popularity;
1944 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1945 Popularity[SI->getSuccessor(i)]++;
1946
1947 // Find the most popular block.
1948 unsigned MaxPop = 0;
1949 BasicBlock *MaxBlock = 0;
1950 for (std::map<BasicBlock*, unsigned>::iterator
1951 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1952 if (I->second > MaxPop) {
1953 MaxPop = I->second;
1954 MaxBlock = I->first;
1955 }
1956 }
1957 if (MaxBlock) {
1958 // Make this the new default, allowing us to delete any explicit
1959 // edges to it.
1960 SI->setSuccessor(0, MaxBlock);
1961 Changed = true;
1962
1963 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1964 // it.
1965 if (isa<PHINode>(MaxBlock->begin()))
1966 for (unsigned i = 0; i != MaxPop-1; ++i)
1967 MaxBlock->removePredecessor(SI->getParent());
1968
1969 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1970 if (SI->getSuccessor(i) == MaxBlock) {
1971 SI->removeCase(i);
1972 --i; --e;
1973 }
1974 }
1975 }
1976 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1977 if (II->getUnwindDest() == BB) {
1978 // Convert the invoke to a call instruction. This would be a good
1979 // place to note that the call does not throw though.
1980 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1981 II->removeFromParent(); // Take out of symbol table
1982
1983 // Insert the call now...
1984 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
1985 CallInst *CI = CallInst::Create(II->getCalledValue(),
1986 Args.begin(), Args.end(),
1987 II->getName(), BI);
1988 CI->setCallingConv(II->getCallingConv());
1989 CI->setAttributes(II->getAttributes());
1990 // If the invoke produced a value, the Call does now instead.
1991 II->replaceAllUsesWith(CI);
1992 delete II;
1993 Changed = true;
1994 }
1995 }
1996 }
1997
1998 // If this block is now dead, remove it.
1999 if (pred_begin(BB) == pred_end(BB)) {
2000 // We know there are no successors, so just nuke the block.
2001 M->getBasicBlockList().erase(BB);
2002 return true;
2003 }
2004 }
2005 }
2006
2007 // Merge basic blocks into their predecessor if there is only one distinct
2008 // pred, and if there is only one distinct successor of the predecessor, and
2009 // if there are no PHI nodes.
2010 //
2011 if (MergeBlockIntoPredecessor(BB))
2012 return true;
2013
2014 // Otherwise, if this block only has a single predecessor, and if that block
2015 // is a conditional branch, see if we can hoist any code from this block up
2016 // into our predecessor.
2017 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2018 BasicBlock *OnlyPred = *PI++;
2019 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2020 if (*PI != OnlyPred) {
2021 OnlyPred = 0; // There are multiple different predecessors...
2022 break;
2023 }
2024
2025 if (OnlyPred)
2026 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2027 if (BI->isConditional()) {
2028 // Get the other block.
2029 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2030 PI = pred_begin(OtherBB);
2031 ++PI;
2032
2033 if (PI == pred_end(OtherBB)) {
2034 // We have a conditional branch to two blocks that are only reachable
2035 // from the condbr. We know that the condbr dominates the two blocks,
2036 // so see if there is any identical code in the "then" and "else"
2037 // blocks. If so, we can hoist it up to the branching block.
2038 Changed |= HoistThenElseCodeToIf(BI);
2039 } else {
2040 BasicBlock* OnlySucc = NULL;
2041 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2042 SI != SE; ++SI) {
2043 if (!OnlySucc)
2044 OnlySucc = *SI;
2045 else if (*SI != OnlySucc) {
2046 OnlySucc = 0; // There are multiple distinct successors!
2047 break;
2048 }
2049 }
2050
2051 if (OnlySucc == OtherBB) {
2052 // If BB's only successor is the other successor of the predecessor,
2053 // i.e. a triangle, see if we can hoist any code from this block up
2054 // to the "if" block.
2055 Changed |= SpeculativelyExecuteBB(BI, BB);
2056 }
2057 }
2058 }
2059
2060 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2061 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2062 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2063 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2064 Instruction *Cond = cast<Instruction>(BI->getCondition());
2065 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2066 // 'setne's and'ed together, collect them.
2067 Value *CompVal = 0;
2068 std::vector<ConstantInt*> Values;
2069 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2070 if (CompVal && CompVal->getType()->isInteger()) {
2071 // There might be duplicate constants in the list, which the switch
2072 // instruction can't handle, remove them now.
2073 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2074 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2075
2076 // Figure out which block is which destination.
2077 BasicBlock *DefaultBB = BI->getSuccessor(1);
2078 BasicBlock *EdgeBB = BI->getSuccessor(0);
2079 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2080
2081 // Create the new switch instruction now.
2082 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2083 Values.size(), BI);
2084
2085 // Add all of the 'cases' to the switch instruction.
2086 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2087 New->addCase(Values[i], EdgeBB);
2088
2089 // We added edges from PI to the EdgeBB. As such, if there were any
2090 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2091 // the number of edges added.
2092 for (BasicBlock::iterator BBI = EdgeBB->begin();
2093 isa<PHINode>(BBI); ++BBI) {
2094 PHINode *PN = cast<PHINode>(BBI);
2095 Value *InVal = PN->getIncomingValueForBlock(*PI);
2096 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2097 PN->addIncoming(InVal, *PI);
2098 }
2099
2100 // Erase the old branch instruction.
2101 EraseTerminatorInstAndDCECond(BI);
2102 return true;
2103 }
2104 }
2105
2106 return Changed;
2107}
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